I, for one, run often FS on an eeepc900 (one year old).
NEver tested max concurrent SIP calls, but for sure is able to run concurrently:
- one FS
- two SIP calls
- two Skypiax calls
- two linux Skype client instances
- two Skype calls
Also, I often use it to generate 6 or 8 concurrent Skype calls.
So, taking account of how heavy Skype is, it probably is able to run
FS with dozens concurrent SIP calls.
Yes you can use Sangoma USB FXO with your laptop. You need to install openzap for this. But for testing you can use this driver. Still there is some issue with Openzap with FS as for as I used. while installing Sangoma USB FXO device you need to use beta drivers.