I spoke with Microsoft last week and they said they are partnering with several SIP-based ITSPs, which will enable Response Point administrators (or VARs) to easily add SIP trunks and move away from analog trunks. You simply use a VoIP account setup wizard in the Response Point Administrator, to connect with Internet telephony service providers (ITSPs) and add new VoIP phone numbers.
The other benefit is the ability to add local phone numbers. Microsoft espoused the need for many small businesses to maintain a local presence. By leveraging VoIP providers businesses can select a local phone number for use in remote locations. Additionally, SP1 adds direct-inward-dial (DID) to directly reach a particular user's extension or pool of extensions.
I asked Microsoft's thoughts on T1 trunks vs. SIP trunks and if they felt the need for T1 support was still there for the SMB, but they wouldn't comment. However, the impression I got was that they might add T1 support in the future. Personally, I think SIP trunking makes more sense for the SMB and it has proven itself cost-effective and reliable. But don't be surprised to see T1 support in the future in RP.
Response Point hardware vendors Aastra Technologies Ltd., D-Link Corp. and Quanta Computer Inc. will ship end-to-end Response Point phone systems, pre-loaded with SP1, this summer. The SP1 release will coincide with Aastra's Response Point phone system debut, which is interesting when you consider Aastra got into the IP-PBX game with a Microsoft IP-PBX competitor last week - the AastraLink Pro 160 appliance, an Asterisk IP-PBX derivative.
Here's a screenshot of the Response Point admin from my review back in November. No doubt the Phone Service portion will have SIP trunks listed when you add them in.
Lastly, check out my Microsoft Response Point review if you haven't read it already to get a feel for this product... It's most note-worthy feature is the speech-recognition capabilities.