https://ofono.org

http://gitweb.merproject.org/gitweb?...fono.git;a=log

Not sure what they are doing with the lower stack yet.

See also:
https://ofono.org/wiki/ofono-supported-modems
https://ofono.org/wiki/how-enable-modem-ofono

In the best case, the modem driver which implements the lower stack would be open, in the worst case that driver would be closed.