Which cloud telephony services support external sip providers?

Question

I've looked at tropo, twilio and cloudvox, plus another bunch.

Most of these services provide their own entry points (PSTN, sip, IM), which is cool.

Unfortunately I already have a local PSTN number that is redirected to a local SIP account. For business, performance and cost reasons (I'm outside the US) I don't want to simply redirect the call on the PSTN number provided by the telephony service. My current provider doesn't support default sip redirection. For performance reasons I don't want to connect an asterisk to the sip account and then redirect to the telephony service (too many legs already)

Do any of these have the ability to act as sip clients and collect calls from external sip accounts?

Answer 1

I think you may find BT's Ribbit will do this.

Answer 2

Twilio can do it but they don't offer it as a self service Option. Write to their support for further help.