Hi,
this is quite interesting project :)
the only issue I may have is Finnish, as I do not understand Finnish,
also not sure if Google API support Finnish, if google can and you can communicate in English (I have done google speech API with English before for both text to speech and voice recognition),
we can do the project with ease,
for phone lines I would recommend VoIP as gsm modems usually add a point of failure and troubleshooting, while VoIP is almost perfect,
kindly let me know if we can discuss the project in details, so I can suggest better price and timelines.
regards,