Glossary · Identifiers
MSISDN
Mobile Station International Subscriber Directory Number
Also known as: mobile number, phone number, E.164 number, A-number
The MSISDN (Mobile Station International Subscriber Directory Number) is the phone number of a mobile subscription — the number other people dial or text to reach it. It follows the ITU-T E.164 international numbering plan and is linked to the subscription’s IMSI in the operator’s subscriber database.
MSISDN structure
An E.164 number is at most 15 digits and is written in international format without the leading + or 00:
| Part | Meaning |
|---|---|
| Country code (CC) | 1–3 digits, e.g. 1 for the North American Numbering Plan or 44 for the UK |
| National destination code (NDC) | Identifies the network or numbering range |
| Subscriber number (SN) | Identifies the individual subscriber |
For example, the UK mobile number written domestically as 07700 900123 becomes the MSISDN 447700900123.
MSISDN vs. IMSI
The two identifiers do different jobs:
- The IMSI identifies the subscription to the network and is used for registration and authentication.
- The MSISDN is the public number used to route calls and SMS to that subscription.
The mapping between them lives in the operator’s HLR/HSS (or UDM in 5G), not necessarily on the SIM. That is why number portability lets a subscriber keep an MSISDN while moving to a new operator and a new IMSI, and why many data-only IoT subscriptions have an IMSI but no MSISDN at all. Some profiles store the MSISDN in a file the device can read, but that copy is often missing or out of date.
Where the MSISDN matters
- Voice and SMS: calls and messages are addressed to the MSISDN. A VoLTE or VoNR call is set up through IMS using SIP and tel URIs derived from it.
- Caller ID: the calling party’s MSISDN is presented to the called party as the A-number.
- Verification and onboarding: many services send one-time codes by SMS to the MSISDN.
Why it matters for testing
Voice and SMS tests depend on the right MSISDN for every profile: a test call to the wrong number, or a caller-ID check against an outdated record, produces misleading results. In SimCheck.ai, each eSIM profile can carry its MSISDN, which is used as the A-number in voice tests — see VoLTE and voice testing.
Last updated · SimCheck.ai team