@SuperDicq @thatbrickster It is not illegal to release modem source code and there is indeed a free software baseband GSM stack (OsmocomBB) and free software LTE implementations (of limited functionality).

Instead, telecom agencies and the patent holders for the protocols will not permit a modem on any network they control unless its IMEI is registered in a big database and the modem contains proprietary malware that disobeys and spies on the user and of course no business is going to release the source code of their malware.

>to make phone calls without paying
Phone calls are really unrelated to LTE networks (as those just transmit IP packets) - the only way to make a phone call is to do SIP and RTP sessions (or a proprietary version of such protocols) through a phone upstream and those are designed to only permit calls from/to approved numbers and also are billed by the minute and therefore running free software on a mobile chipset won't allow you to make phone calls without paying.

>or jam the network or something.
All you need is a radio jammer on the LTE frequencies to jam the network, which can be easily bought online.

Attacks against vulnerable LTE baseband implementations are possible, but all making everything proprietary does is slow down malicious attackers a little bit (who won't hesitate to use any illegal means possible to get up to speed), while ensuring that security researchers are slowed or stopped from finding vulnerabilities and responsibly disclosing them (with the end result being only negatives for security).