Sizing blue lines for an ecommerce support inbox before peak season

Most stores decide on iMessage support the same way. Someone sees a blue bubble with a business name and photo on their own phone, decides the store should have that too, and buys one line. Then the week after Black Friday arrives, the line runs out of new conversations by mid-afternoon, and the "your order is delayed" texts stop going out blue.

A blue line has hard daily limits. Those limits make capacity planning straightforward if you do it before peak season. This guide turns the limits into a sizing formula, works through a cost model for one peak month, and covers what a blue line won't do for you, so you can plan the regular-number side of your setup alongside it.

What a blue line is, in one paragraph

A blue line sends your texts as iMessage, so they show up blue on iPhones with your business name and photo. It doesn't need 10DLC registration, so you can start texting as soon as the line is set up. Texts to Android phones go out from your account's regular number. If you already had one, they bill at the regular text price. If you don't have a regular number yet, a blue line comes with a green one, and once the account registers, its texts bill at the blue-text price of 6 cents a segment. Replies, reactions, typing indicators and group chats all land in the same inbox thread as SMS, so your support team works one queue. A blue line can also text first, which is how it differs from Apple Messages for Business. That service only lets the customer start the chat. We cover that difference in iMessage for business vs Apple Messages for Business.

The four limits that drive sizing

Two of these limits shape how you write support messages more than how many lines you buy.

The 2-text rule. A delay notice plus one follow-up is your budget. If you would normally send three texts (a notice, a tracking update, a "still waiting?"), rewrite the first one so it asks a question that invites a reply: "Your order #1042 is running 3 days late. Reply 1 to keep it, 2 to cancel." Once they answer, the thread is open and the cap no longer applies.

Photos after a reply. Lead with text and ask for a response before you send images. It costs one extra exchange, and the photo arrives in a thread the customer has already engaged with.

A planning note: the 50 cap applies to conversations your line starts. If you're unsure how a thread that a customer opens is counted on your account, check the blue line guide in our docs for the current rules. The worked example below assumes conservatively that every new person counts.

The sizing formula

Here is the formula, step by step:

1. Count new outbound conversations on your worst day. Use last year's peak: delay notices, address problems, out-of-stock substitutions, return follow-ups. Count people, not messages. Plan for the worst day, not the average.
2. Multiply by your iPhone share. Android customers fall back to your regular number and never touch blue-line capacity. Pull the share from your storefront analytics instead of guessing.
3. Add a buffer. Peaks are lumpy. A shipping carrier delay can double one day's outreach. A 20% buffer is a reasonable starting assumption.
4. Divide by 50 and round up. That's your line count.

In one line: lines = ceiling(worst-day new conversations × iPhone share × 1.2 ÷ 50)

Worked example

These are assumptions for illustration, not benchmarks:

• Typical peak day: 150 new outbound conversations
• Worst day (the week after Cyber Monday): 260 new outbound conversations
• iPhone share from analytics: 55%

Worst day: 260 × 0.55 = 143 iPhone conversations. With a 20% buffer: 143 × 1.2 = 171.6. Divided by 50 that's 3.43, which rounds up to 4 lines.

On a typical peak day, the same math gives 150 × 0.55 × 1.2 ÷ 50 = 1.98, so 2 lines cover it.

You have two reasonable ways to handle the gap:

• Buy for the worst day. Four lines sit partly idle most of the month, but outreach never stalls.
• Buy for the typical day and turn on "Add lines automatically." When a day's new conversations are used up, it adds a line. This is a safety valve, not a free one: every line it adds is another $99 a month. If it fires twice in December, you end up with four lines anyway, just added later.

If your worst day is a known date, such as a planned shipping cutoff or a launch, buying the lines ahead is usually cleaner than relying on auto-add.

The cost model

A blue line costs $99 a month per line, plus 6 cents a segment for each text sent. Replies to a blue line are also 6 cents a segment. Reactions are free. Android traffic goes through your regular number at the Standard rate of $0.0075/segment plus a $0.0045 carrier fee per segment. Replies you receive on the regular number are billed the same way as texts you send. That assumes your store already had a regular number: if your green number came with the blue line, Android and campaign texts bill at 6 cents a segment once you register, and the Android rate below is three times as much.

The monthly formula:

($99 × lines) + (blue segments sent and received × $0.06) + (Android segments sent and received × ($0.0075 + $0.0045))

Ready's all-in prices per segment include the carrier fee but not screening: Scrub lists and Number validation, the two switches in Settings under Compliance, each add $0.003 per segment when switched on, shown as screening on your bill, and both are off by default. Unless you turn the opt-out footer off, the first text to each contact, and one again from time to time, also gets "Reply STOP to opt out" and your business name if the message does not already have them, so a text close to the segment limit can bill one more segment.

One peak month, worked out

Same store, 4 lines for the month. Assume:

• 4,000 iPhone conversations in the month (new and existing threads)
• 3,300 Android conversations
• An average of 10 segments per conversation, both directions combined

Blue line:

• Lines: 4 × $99 = $396
• Segments: 4,000 × 10 = 40,000 × $0.06 = $2,400

Android on the regular number:

• Segments: 3,300 × 10 = 33,000 × $0.0075 = $248
• Carrier fees: 33,000 × $0.0045

Total: $3,044 plus 33,000 × $0.0045 in carrier fees. This figure doesn't include the compliance surcharge. If scrubbing or landline validation is switched on for the account, each adds $0.003 per segment. Both are off by default.

What the blue bubble costs you

Run the same iPhone traffic over SMS instead: 40,000 × $0.0075 = $300 plus 40,000 × $0.0045. The blue line version is $396 + $2,400 = $2,796. Ignoring carrier fees, you're paying roughly $2,000 extra for the month to have those 4,000 iPhone conversations show up blue, with your name, photo and typing indicators.

We won't promise that difference pays for itself. We don't publish a measured reply-rate lift for blue lines. Teams turn them on because a branded iMessage thread looks like a conversation instead of an automated notification, and in support that's what you want customers to feel. Whether that's worth about $2,000 in your peak month depends on your order values and what a slow-to-resolve ticket costs you. For a broader look at when blue beats green, see blue bubble texting for business.

Keep support replies short

Every segment costs money on both sides of the line, and on blue it costs three times the Standard SMS rate. On the Android side, standard segment math applies. A GSM-7 text fits 160 characters in one segment, and longer texts split into 153-character segments. A single emoji drops the limit to 70 characters (67 per segment when multipart). A 140-character reply with one emoji is 3 segments instead of 1. Ready swaps curly quotes, long dashes and ellipses for plain ones before sending, so those don't inflate the count. Emoji do.

What a blue line doesn't send

Campaigns and drip campaigns send from your regular numbers, not the blue line. Your Black Friday promo, your abandoned-cart drip campaign and your back-in-stock announcement all go out green, at $0.0075/segment plus $0.0045.

This affects planning in two ways:

• Your regular number still needs registration. The blue line skips 10DLC, but the regular number handling Android support and every campaign doesn't. Registration runs $25/mo and $2 per number. The charge at submit is the first month's $25. Most approvals take 2 to 7 days, so submit well before your first peak campaign, not the week of it. Unregistered traffic gets carrier-filtered.
• Don't count campaign volume toward line sizing. Blue line capacity is for one-to-one support and outreach only. A 20,000-contact promo doesn't touch your 50-a-day caps.

For how blue and green traffic share one thread and one API, see SMS API with iMessage: one thread for blue and green texts. The request shapes are in the blue line API docs.

Compliance doesn't change because the bubble is blue

Support texts still need consent. A customer who opted in at checkout for order updates has agreed to order updates, not to every message you might want to send. Ready handles the mechanics:

• STOP and UNSUBSCRIBE are honored automatically, and the opt-out propagates across campaigns.
• Sends are held outside permitted local hours, based on the recipient's area. Campaigns, drip campaigns and automations wait up to 24 hours for the window; a one-to-one or API text is held only if the window opens within 6 hours, otherwise it is not sent, and you send it again once the window opens; a one-to-one reply to someone who texted you in the last 24 hours goes out at any hour.
• When you send through the API, consent_attested records your attestation for each send.

That attestation is not a per-contact consent record. Your store keeps the opt-in time, wording and page. Compliance is ultimately the sender's responsibility. For the full checklist, see ecommerce SMS compliance tools.

When not to buy a blue line

Be honest with yourself on these:

• Your audience skews Android. At a 30% iPhone share, most of your support runs on the regular number anyway, and $99 a line buys very little.
• Support is almost all inbound and low volume. If you open a handful of threads a day and most customers email, Standard SMS on a registered number does the job for less.
• You mostly need marketing reach. Blue lines don't send campaigns or drip campaigns, so they don't help there.

The practical takeaway

Size against your worst day's new outbound conversations, multiplied by your iPhone share, with a buffer, divided by 50. Price the month as lines × $99, plus 6 cents per blue segment both ways, plus Standard SMS for Android. Start registration for your regular number well ahead of peak, because campaigns depend on it.

If you want to test this before November, set up one line, run your current support volume through it for a few weeks, and check the new-conversation count against the cap. You can sign up here, and the per-segment rates are on the pricing page.

Frequently asked questions

How many blue lines does an online store need for the holidays?

Take your worst day's new outbound conversations, multiply by your iPhone share, add a 20% buffer, divide by 50 and round up. Each line can start up to 50 new conversations a day, while texting with people you already talk to is unlimited. For example, 260 new conversations at a 55% iPhone share works out to 171.6, which means 4 lines. Android customers go through your regular number and don't use blue line capacity.

What happens when a blue line runs out of new conversations for the day?

It can't start any more new conversations that day, so reaching more new people means adding another line. The "Add lines automatically" setting can add one when the day's new people are used up, but each added line is another $99 a month. Existing threads keep working, since texting people you already talk to is unlimited. If your worst day is a known date, like a shipping cutoff, buying the lines ahead is usually cleaner.

Do you pay for customer replies on an iMessage business line?

Yes. A reply to a blue line is billed at 6 cents a segment, the same as a text you send. Reactions are free, and each line also costs $99 a month. Texts to Android phones go from your regular number at the Standard rate of $0.0075 a segment plus a $0.0045 carrier fee, and replies there are billed the same way as sent texts. If your regular number came with the blue line, those texts bill at 6 cents a segment instead. Keeping support replies short keeps the segment count down.

Does a blue line need 10DLC registration?

No. A blue line doesn't need 10DLC registration, so you can start texting as soon as it's set up. Your regular number still needs it, because that number handles Android support and every campaign and drip campaign. Registration runs $25 a month and $2 per number. The charge at submit is the first month's $25. Most approvals take 2 to 7 days, so submit well before peak season.