Of course, this isn't a totally new idea. While I was at Qualcomm, someone hacked together a plastic concept model of what was termed the "bachelor phone". It was a common Lucent-branded desktop landline phone with a slot where the speed-dial keypad should be. Drop a 5GP (QCP-860/1960) into the slot and that phone drop the landline and route calls through the cell.
Except, of course, it didn't give that capability to the rest of the house. See, bachelors only have one phone in their house. And they stay within three feet of it while talking. Yeah.
The project never went anywhere. If I had to guess, someone up the chain figured it wasn't worth the money for them to produce with the features the Cellsocket currently offers (which I thought were Intuitively Obvious.) Which would've been true... The 5GP was a very popular CDMA phone at the time, but its connector wasn't shared with any other QC phone, let alone competitors. Motorola got smart (a bit before Qualcomm-becoming-Kyocera did) and standardized its charge/HFK/data port. One unit serves a legion of phones by simply changing a piece of cheap injection-molded plastic.