Most "which messaging channel should we use" debates skip the question that decides most of them: who is allowed to send the first message, and what does the customer need on their phone for it to arrive? SMS, Facebook Messenger and WhatsApp differ much more on those two points than on features. Once you know the answer for your use case, the choice is usually obvious.
This post compares the three on reach, consent, who starts the conversation, cost model and fit. We make Ready, a texting platform, so we have a stake in SMS. That is the reason to be precise about where the chat apps win. In several of the cases below, they do.
The short version
- SMS reaches any mobile number with no app required, and the business can text first if the person opted in. In the US it requires carrier registration (10DLC), and you pay per segment.
- Messenger reaches people who use Facebook and have already messaged your Page. The customer starts the conversation. It works well as a support and inquiry channel and poorly for outbound reminders.
- WhatsApp reaches people who have WhatsApp and opted in to hear from you on it. The business can start a conversation, but only with pre-approved templates. It is strong in countries where WhatsApp is the default messaging app and weaker in the US, where native texting dominates.
Side-by-side comparison
| SMS (10DLC) | Facebook Messenger | WhatsApp Business Platform | |
|---|---|---|---|
| What the recipient needs | Any mobile phone number | A Facebook/Messenger account | WhatsApp installed |
| Who can start the conversation | Business, with prior consent | Customer (business replies inside a time window) | Business, using approved templates, with opt-in |
| Free-form replies | Anytime within consent and quiet hours | Within the standard messaging window after the customer's last message | Within the 24-hour window after the customer's last message |
| Registration | Brand + campaign registration with carriers | Facebook Page + Meta app review for API access | Meta business verification + template approval |
| Cost model | Per segment (sent and received) | Generally no per-message fee from Meta | Meta charges per message/conversation, varying by country and category |
| Rich media | MMS pictures; plain text is the default | Images, buttons, carousels | Images, documents, buttons, lists |
| Best fit | Reminders, alerts, follow-ups, US customers | Inbound inquiries from social and ads | International customers, rich support flows |
Meta changes its messaging policies and pricing often. Check its current documentation before you build anything that depends on a specific window or fee. We don't quote Meta's rates here because they shift and vary by country.
Reach: the phone number is the universal address
Almost every customer record you have includes a phone number. Far fewer include a confirmed WhatsApp account, and none include a Messenger thread unless that person messaged your Page first.
That is SMS's main structural advantage. You don't have to know which apps someone uses. If they have a mobile number and agreed to hear from you, the text arrives in the app they already check, and nothing needs installing.
The picture changes outside the US. In many countries in Latin America, Europe, Africa and South Asia, WhatsApp is the default way people text each other. If most of your customers are there, WhatsApp can beat SMS on reach and on how familiar the conversation feels. Ready is US-focused (10DLC is a US carrier system), so a business with a mainly international audience should take WhatsApp seriously.
Messenger has the narrowest outbound reach, because the customer has to open the door first. In exchange, it has the warmest inbound traffic: someone who clicked "Send message" on your ad already wants to talk.
Consent and who can text first
This is where the channels differ most.
SMS
In the US, texting is governed by the TCPA and carrier rules. Marketing texts need prior express written consent, and every text has to honor STOP. Carriers also require you to register your brand and campaign before they will deliver business traffic reliably. Unregistered traffic gets filtered. Our 10DLC explainer covers the mechanics, and 10DLC rules and requirements covers what carriers actually check.
Once that is done, the business can start the conversation. That matters for anything time-driven, such as appointment reminders, delivery updates and payment notices.
Cold contact is a different matter. Texting a purchased or cold list is how businesses end up in TCPA trouble. Use phone and mail for cold outreach, and send SMS to people who opted in or replied.
Messenger
The customer messages first, and you reply within Meta's standard messaging window. Outside that window, Meta allows only narrow follow-up cases. Messenger can't send "your appointment is tomorrow" to someone who has never messaged you.
You can start a conversation, but only with a template Meta has approved, and only with someone who opted in to WhatsApp messages from your business. Once they reply, you get a 24-hour window for free-form messages. The template system works, but it adds an approval step to every new outbound message type.
Across all three channels, compliance is ultimately the sender's job. Platforms can reduce risk, but none of them makes you immune to it.
Cost: different models, not just different prices
Messenger is generally free per message, which is its real advantage for high-volume inbound support. WhatsApp charges per message or conversation on a rate card that depends on country and message category. SMS charges per segment.
SMS pricing is the easiest of the three to model, so here is a worked example on Ready.
Example assumptions: a 1,000-contact appointment-reminder list, opted in, with one reminder each. The message is 150 characters of plain text, so it fits in one segment (the limit is 160 GSM-7 characters). About 30% of recipients reply, which is a round assumption and not a measured figure.
- Outbound: 1,000 × 1 segment × $0.0075 = $8 plus 1,000 × $0.0045 in carrier fees
- Replies: 300 × 1 segment × $0.0075 = $2 plus 300 × $0.0045. Replies are billed like sent texts.
- Registration: $25/mo for registration + $2/mo per number.
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.
Segments are where SMS budgets go wrong. Adding one emoji drops the limit to 70 characters per segment (67 in multipart). The same 150-character reminder with a 🎉 becomes 3 segments, which triples the outbound cost. Ready swaps curly quotes and long dashes for plain ones before sending, so those don't change the count, but emoji do. If you are comparing SMS costs across vendors, 10DLC cost: every fee explained lists everything you will actually pay.
Ready's Standard rate is one flat rate, and it is not the lowest per segment on the market. Raw carrier APIs such as Twilio (around $0.0083/segment) and GoHighLevel's LeadConnector (around $0.0083/message) charge less per message. With Ready you get self-serve registration (most approvals take 2 to 7 days) plus the inbox, campaigns, automations and compliance tooling in the same account.
Fit: which channel for which job
Pick SMS when
- The business needs to start the conversation (reminders, shipping, billing, follow-up on a form fill).
- Your customers are mainly in the US.
- You can't assume any particular app is installed.
- You want quiet-hours enforcement and STOP handling to work by default. On Ready, campaign and automation sends outside permitted local hours are held and go out later (a one-to-one or API text is held only if the window opens within about 6 hours, otherwise it is refused), and an opt-out blocks that contact across every campaign.
Pick Messenger when
- Most of your leads come from Facebook and Instagram ads with a "message us" button.
- The work is answering questions, not sending notices.
- You want a free channel for high inbound volume and can accept that you can't start conversations.
Pick WhatsApp when
- Your customers are in countries where WhatsApp is the default.
- You need rich support flows with documents, buttons and lists.
- You can live with template approvals for outbound messages.
Most businesses end up using more than one channel. A common setup is Messenger for inbound ad leads, then SMS once the lead shares a number and opts in, because SMS is the channel you can follow up on reliably. We cover a similar split between app notifications and texts in SMS vs push notifications.
The iPhone option: a blue line
US businesses often want a WhatsApp-style experience: rich, branded and conversational, but without asking customers to install anything. That is the gap Ready's blue line fills. It sends iMessage from your business, so texts appear blue on iPhones with your business name and photo.
How it works:
- Price: $99 a month per line, plus 6 cents a segment for each text sent. Replies are also 6 cents a segment, and reactions are free.
- No 10DLC registration needed. You can start texting as soon as the line is set up.
- Limits: unlimited texting with people you already talk to. Each line can start up to 50 new conversations a day, send up to 2 texts to someone until they reply, and send photos only after a reply.
- Android: texts to Android phones go from your regular number. If you already had a number they bill at the regular text price; if the blue line came with its green number, your account's texts bill at 6 cents a segment once you register or send through GoHighLevel.
Campaigns and drip campaigns send from regular numbers, not the blue line, so the blue line is for one-to-one conversations rather than bulk sends. Unlike Apple Messages for Business, a blue line can text first. The difference is explained in iMessage for business vs Apple Messages for Business. Setup is covered in the blue line guide.
For platforms building messaging into a product
If you run a CRM or vertical SaaS product and are deciding which channel to offer your customers, SMS is usually the first to ship, because every customer has phone numbers in their records. The work is in registration: each of your customers needs its own brand and campaign. Ready handles that through sub-accounts, each with its own numbers and 10DLC registration, behind one REST API (POST /v1/messages, with consent_attested recorded per send). Start with the quickstart and the messages API reference.
Messenger and WhatsApp each need their own Meta integration, business verification and policy reviews per customer. If your users ask for them, budget that work separately.
The practical takeaway
Choose based on who starts the conversation and where your customers already are:
- SMS if you need to start the conversation with US customers.
- Messenger for inbound inquiries from social traffic.
- WhatsApp if your audience lives on it.
- A blue line if you want branded, rich conversations with iPhone users without registration.
If SMS is on your list, try it before committing. Ready's first 20 texts are free one-to-one sends, so use them before you register (a card on file is required to send). You can sign up here and see how replies land in the inbox.