Cogent(www.cogentph.com) may have what you're looking for. Most of their ads on PC Buyer's Guide advertise a GSM gateway -- i.e. "Make your GSM line into a PABX trunk line". Baka meron silang mas simple na unit.
You can also try i-Globe Technologies(www.routers.com.ph); they seem to be selling a lot of generic China made stuff...primarily routers, load balancers and such, but i wouldn't be surprised if they carried GSM desk phones.
Last time i visited was way back in 2003; dunno if they're still at the pc hub at Gilmore(cor. Aurora Blvd.)
hi HP. we need to have those phones in a specific area only. we like them precisely because they are not portable and can only be conveniently used within the office premises. aside from that, their antennas provide for better signals.
i also need one unit for use in my mother's room (she's 84, btw). the bigger keys in the desktop unit may be more suitable for her than the mobile's keypad.