I would not. If the modem was ever open source hardware it would never be permitted to attach to the major networks. There's always a catch. There is just too much collusion between wireless carriers and governments, having built out one of the first GSM network in the US in the 90's. The capabilities were wild back then and I can only imagine all the undocumented capabilities now. I only learned about the capabilities having worked around a lot of drunk Swedish telco switch mainframe developers.

Having said that, I would love to have a truly open source phone that I could load any bog standard Linux distro and all the drivers have been reviewed by Linus without him ever once feeling the urge to lift the middle finger. I would only be using it for non sensitive voice and text.