Can I configure my soft phone to work with the Twilio SIP endpoint?

Twilio SIP Registration is actively being developed to be released soon.  If you are interested in signing up for early access via our Developer Preview, you can do so here:

http://ahoy.twilio.com/sip_programmable_voice

In the meantime, in order to send traffic to a SIP device such as a soft phone, that device must have a valid SIP Address of Record (AOR), provided by a SIP registrar. Twilio is not presently a SIP registrar and does not currently provide SIP Registration, so you cannot use the sip.twilio.com addresses generated in your account on a SIP device/VoIP phone.

As such, you would need to use an external SIP provider that provides SIP registration. From this provider you can make calls to Twilio SIP Endpoints or receive calls from Twilio to your registered SIP address.