A system for assisting a user in selecting a packet-based telephony service provider ("PBTSP") from a group of PBTSPs, and in registering the user with the selected PBTSP for outbound and/or inbound calling. The selection of a particular PBTSP may be stored in a database, and this stored information may be used to enable the user to exchange telephone call data with one of the PBTSPs. One preferred system receives data from the user's computer device, determines whether the user is registered with one the PBTSPs and, if so, transmits data to the computer device which enables it to exchange telephone call data with one of the PBTSPs. The system also receives telephone call data from the computer device, accesses contact information for a PBTSP, and transmits the received telephone call data to the PBTSP using the accessed contact information.