SMS and messaging APIs

SMS and messaging APIs let your application send and receive text messages: sign-in codes, order and delivery alerts, appointment reminders, support conversations and marketing. Product and engineering teams wire them into their apps, and most also offer MMS and other channels such as WhatsApp, RCS or voice on the same account. In the US a text carries three layers of cost: the vendor's per-message rate, a carrier fee per message passed through from AT&T, T-Mobile, Verizon and others, and A2P 10DLC registration fees set by The Campaign Registry for sending from ordinary local numbers. The APIs differ in how much of that they publish, how you buy (pay as you go online, or through sales with a minimum), which compliance documents cover messaging, and how much of opt-out handling and registration they do for you.

We compare them on the same six indicators, read from each vendor's pricing, fee, security, legal and documentation pages:

• Pricing clarity: whether the per-message rate, carrier fees per carrier, 10DLC fees, per-country prices and volume tiers are published and can be bought online, and whether the pages leave prices out or contradict themselves.
• Free trial: trial credit and whether it needs a card, free test credentials or a sandbox, and texts included free every month.
• Price for 10,000 US texts: the lowest listed monthly cost to send 10,000 single-segment texts to US mobile numbers from one registered 10DLC number, carrier and registration fees included, with the arithmetic shown; 0 when the pages do not publish the rate or the carrier fees.
• Compliance documents: the vendor's own SOC 2 Type II, ISO 27001, a HIPAA BAA for messaging, a GDPR DPA and a data region outside the US.
• Messaging features: delivery and inbound webhooks, STOP and HELP opt-outs handled by the platform, a verification (OTP) API, 10DLC registration through the API and official SDKs.
• Team access and support: SSO, team roles, two-factor login, an audit log, paid support plans with published prices and support for every account.

Delivery rates, throughput and send speed depend on carriers and registration status, so we state published limits where a vendor does but do not score them. Each review says which pages it was written from and when. Where we have run a product hands-on, the evidence is on its page.