Except when it's a CDMA carrier and phone, such as Verizon or Sprint. Then the phone is the account.

The iPhone 5 is an LTE "world phone" by Verizon's standards. It means that at home it sits on CDMA (Voice, text and slow data) with the phone being the account, then also sits on Verizon's LTE (fast data) network using the SIM as the account.

If the SIM is pulled and replaced with a GSM or other LTE carrier, then the CDMA side of the phone shuts down, and the voice, text and data accounts all are pulled from the SIM.

Overall I'm glad that the CDMA tech path is a dead one, and all CDMA carriers worldwide are migrating to LTE long term. Once they start using voice over LTE and deactivate the CDMA networks, the concept of a phone being the account goes away entirely.