Inclusion Criteria:  Registered to receive ART (this includes patients receiving ART through multi-month scripting) at selected study sites. Aged ≥18 years. Have a documented cell phone number in their clinic records Are eligible to receive appointment reminders as part of routine care OR eligible to receive follow-up text messages as part of routine care for missed clinic appointments.  Exclusion Criteria:  Do not have contact details in their clinic records. Have contact details on record that are established to belong to someone else upon follow-up (i.e., wrong number). Have contact details that are deactivated/non-functional (i.e., voice notification that the number does not exist). Are documented to have self-transferred out of the clinic. Are known to have been deceased.