MSISDN

MSISDN is the technical name for a phone number itself, in international format: country code plus national destination code plus subscriber number, capped at 15 digits under the ITU-T E.164 standard. +91 98XXXXXXXX is an MSISDN it's the number you dial and text.

• Why it matters: it's the single most common cause of "message not delivered" that has nothing to do with the network. Drop the +91, leave a trailing 0, or store the number with spaces or a dash, and most APIs reject or misroute the message before it reaches an SMSC. It's also the field your sender ID and templates are validated against under DLT compliance.

• Often confused with: an IMSI, which identifies the SIM card itself and stays fixed even when the phone number ports to a new operator. The MSISDN is what you dial and text; the IMSI is what the network uses internally to authenticate the SIM.