I've been keeping a watchful eye on LibreTel, Jeff Pulvers DID to SIP service.
LibreTel just went into beta with their Port of Call service and is offering phone numbers in Israel, the UK and selected USA cities. Once you have a LibreTel number you can point it to a FWD sip phone, so if you're using either the FWD softphone or are in the Pulver Communicator beta group you can now give people who are PSTN based the LibreTel phone number so they may call you.
This all is about presence and devices being SIP aware. What Pulver and his LibreTel are basically creating is a SIP switchboard operator that allows people who need to be found to be reached, regardless of the platform or device. Keep an eye on this company and watch how they marry up services and software.
I like it !