Recipients are de-duplicated by phone number, so a customer in several selected groups only gets one message. In the current version, every group — Plan Groups, SMS Lists, and all of the Global/modules/Delivery/Pickup/Pickup Locations groups — skips anyone with no phone number on file and anyone whose Receive SMS? preference is off (for SMS-list contacts that aren't customers, only the phone-number and Receive SMS checks apply, since they have no account to suspend). Most groups (SMS Lists, all Global entries, modules, Delivery, Pickup, and Pickup Locations) also skip suspended accounts; the Plan Group (subscription-based) groups do not re-check suspension status at send time, so a suspended customer with an active/paused/cancelled subscription can still be included if their Receive SMS preference is on. If a customer you expected is missing, check their phone number and their Receive SMS setting first.