Caller IDs are one of the pieces of information that are passed from carier to carrier when a call is placed. Carriers can have different caller ID formatting and, as calls may traverse through several networks before reaching Twilio, the information may be altered along the way.
There are three main circumstances that cause a caller ID to be misdisplayed:
- The originating carrier may not correctly format or send the original From number. Refer to this article for information on restricted/blocked caller IDs.
- A caller ID may be modified along the way by any intermediary carriers
- The caller ID may be lost or replaced* when crossing international borders
When Twilio receives an incoming call, we perform basic normalization to E.164 formatting. Otherwise, we will pass along the information exactly as we receive it to your application. It is currently not possible to discover the real caller ID once it has been altered by carriers.
* For international calls, local regulations sometimes dictate that a caller ID be modified. We see this especially often with calls from Australia, for instance. Another example of this modification occurs when calls are initiated outside of the USA to Twilio toll-free numbers.