your question can be a bunch of things. If you mean recieving caller id, then asterisk needs to GET the data from somewhere. This can be the caller-id service on your phone line, or in the case of a VoIP call, the caller-id is sent along with the call data. This data comes from the extension or account number of the phone, along with a name field which is configurable on the phone itself. Asterisk can override this and set the phone’s outgoing caller id to be whatever you want. However, just because asterisk sends it doesn’t mean it gets heard. A POTS analog channel has no method of sending outbound caller ID, the outgoing caller ID is set by the phone company. Also, many VoIP providers will ignore your outbound caller ID and set it themselves. PRI channels usually let you set outbound caller ID but not always.
Does that help?