Some thing like a SIP to digital, I have been asking providers for such devices, I am looking for SIP to Anolgue.
We use Nortel CS1k as our PBX and they will soon release updated software that will allow you to use OCS for call control but keep you Nortel desk phone. Personally we won't be doing it OCS all the way it rocks!!!!
i am sure thast other PBX's manufactures either are othering something like that now or soon will, as they move towards the "Plan A" type of gateway.
Blackduke