Short answer: keep the password-reset template, expiry policy, and delivery-state mapping inside the startup app; compare SMS services only after that boundary is fixed, using the actual US and EU sender-registration path, per-message segment count, and receipt-retrieval method for your traffic.
That decision makes the provider replaceable without pretending every provider behaves alike. The application creates a single-use reset URL, renders a short message, submits it through a narrow adapter, and records the provider's opaque message ID. A worker then polls through that same adapter until the message reaches a terminal state or the application's polling budget ends. Registration and billing stay provider-specific. Reset semantics don't.
This is a template-ownership problem first.
Govern the password-reset message as a release artifact
Own the meaning of the message in application code: which event caused it, which variables are allowed, how long the reset token remains valid, and which text version was sent. Let the SMS service own transport details such as sender eligibility in a destination and the raw delivery status. The adapter translates those raw statuses into a deliberately small internal vocabulary.
