My laptop (a Thinkpad T440) has a SIM card slot which is meant to be used for Internet, though I haven't tested that yet since I don't have any SIM cards with Internet contracts.
However, is it possible to use my laptop as a phone with a SIM card? Or would I need a different antenna for that?
EDIT: Oh, and I'm running Arch on it (in case that makes a difference).
This is more of a high level bash at an answer.
The android project largely got merged into the linux kernel a while back. I suspect the first step is to review what all was included in those merges. You would have to recompile the kernel to accommodate those changes. I think they largely included things to make a stable system stallable, phones are toggled on and off all the time servers are not.
The next step should check that the linux drivers for that chipset accomodate the functionality you need to enable. If so there is a high chance you could enable calling. You may have to read up on the driver to enable actually calling and so forth.
I have a suspicion that it might actually be quite trivial to get right if you can send AT commands to the chip you should be able to make it dial out or respond to calls. Then the trick is to connect the microphone and speaker to the connections it it opens. Given that it is linux it might even be as trivial as piping your microphone device to the phone chips transmitter but I'm just taking a guess at that.
Yes, at least some chips commonly found in 3G/4G modem (e.g. Huawei) are able to be put into a voice-compatible mode by using so-called 'ussd'-codes.
But, then you'll have the problem nwilder mentioned: No packaged software for in the repos.
