The Cisco Voice Gateway connects directly to PBX's or public telephone networks to carry voice traffic accross IP networks - by converting IP calls to standard telephone calls and vice versa. 

The Cisco VG248 voice gateway is rack mountable.  Each one can support up to 48 analog telephone lines, allowing users with a large number of analog phones to access IP Telephony without having to replace all their handsets.

The VG248 will still support all existing analog features such a caller ID, message waiting lights and feature codes, so the old analog phones will work just as before.