Links to related resources
Some free telephony projects:
FreeSwitch
(uses SpanDSP)
BareSIP
(uses SpanDSP)
Bayonne
OpenSIPS
(was OpenSER)
Kamailio
(was OpenSER)
SIP Foundry
Asterisk
(optionally uses SpanDSP)
Some makers of dumb (or nearly dumb) telephony hardware:
Atcom
OpenVox
Sangoma
Xorcom
Digium
Pika Technologies
Redfone Communications