Both NetMeeting and OpenH323 can interoperate with Cisco's voice capable routers. To successfully initiate calls from a Cisco to an OpenH323 (i.e, Linux) client, the G.711 codec must be explicitly specified. For example, with the following configuration, dialing "911" on the Cisco will place a call to a Linux system (10.1.1.1) running OpenH323:
dial-peer voice 911 voip destination-pattern 911 session target ipv4:10.1.1.1 codec g711ulaw
To call from Linux to a Cisco, use ohphone with a number@host argument. number should be a phone number that's been configured on the Cisco using a dial-peer statement. For example, this will call number "111" on a Cisco (10.1.1.10):
bash$ ohphone -n email@example.com
To call from NetMeeting to a Cisco, select the Cisco as a gateway. To do this from NetMeeting, select Tools->Options. For NetMeeting 2, select Audio, check the box labeled "Use H.323 gateway", and enter the Cisco's DNS or IP address. For NetMeeting 3, select General+Advanced Calling..., check the box labeled "Use a gateway..." (not gatekeeper) and enter the Cisco's address. Now, you can type a phone number directly into NetMeeting's address panel and it will be relayed to the Cisco and resolved there, using the Cisco's configured dialing rules. If you're using NetMeeting 2, you'll need to select "H.323 Gateway" from the "Call using:" list when you initiate the call.