I have a fancy box that implements a "voice attendant" for our home phone. Colleagues have duplicated it for use on their home and office phones (whether land line or VoIP).
Recently, a colleague tried to implement it on a cell phone line using a box like this:
as a bridge/gateway between the cellular network (with his cell phone acting as intermediary). He's had all sorts of problems. :<
Given the successes others have had, I suspect the problem lies in the bridge device.
As I've not yet designed my own telco interface (using a COTS FXS), my interest lies in determining whether there is some "enhanced" set of POTS specifications that *my* FXS should embrace... or, if this is just a "suboptimal implementation" -- in which case, my colleague is SoL.
The device referenced should be simple enough to implement. I'd imagine the online comments I've seen about it (low volume, weak ringer, garbled sound, etc.) are likely consequences of designing "on the cheap" and/or relying on stealing charge current from the cell phone's charger/power source.
Anything I should have him look at, specifically? Or, pointers to another COTS solution (or, an open-hardware implementation!) of something similar that he could pursue? Or, just let him wait until I come up with a fresh implementation (LOW on my priority list as targeted users have tethered lines)