There appear to be two approaches to telephony using VoIP. The first is that used by network hub and router manufacturers such as Cisco and 3com. Their systems are analogous to conventional switches where incoming trunks enter a central device, which connects to a number of handsets. Calls and their associated data (CLID, dialled number etc.) can be picked up from the incoming ISDN trunks or the digital pairs to the handsetss . Most users prefer extension-side recording since management can select which agents need to be recorded and, once connected, all extension-side calls are logged. Electrodata's Direct Digital Connectivity solutions (DDC) pick up voice, and call data without the added expense and complexity of accessing the CTI port on the switch.

In the Cisco/3com VoIP equivalent system, a conventional trunk-side ISDN connection is made however the proprietary signal to the digital handsets is replaced by a VoIP standard, typically H323. We can also record all calls at the ISDN trunk and work is presently well advanced for "sniffing" calls on the network connecting the handsets.

Proprietary VoIP architectures are being developed by many of the large PBX suppliers, such as Avaya, Nortel, and Siemens etc. These provide for connection to the conventional telephone network via ISDN, plus the ability to establish direct connections between handsets via an Intranet bypassing the ISDN and the switch. With this latter approach, the “switch” is only used to monitor the details of the direct calls. Providing encryption of the VoIP signals is not used, it is feasible to also sniff packets between handsets. If encryption is used, the switch supplier must provide a decrypted "conference" call to the recorder for each call being recorded.

If recording is vital to your enterprise and you wish to have encryption added to calls, make sure your VoIP switch supplier is able to provide the required feeds to a recorder.