Oh, sorry - missed it in the FAQ. My understanding (which isn’t particularly well researched) is that any 3G or 4G packet data requires implementing algorithms (compression and error corection stuff) which are unfortunately encumbered with software patents, and cannot be implemented in a FOSS manner unless someone paid the licensing fees for everyone (similar to Cisco paying the H.264 patent fees for OpenH264), or the patent pool gets bored and relinquishes their patents.

When do the patents expire?

Unsure - https://en.wikipedia.org/wiki/LTE_(telecommunication)#Patent... is pretty depressing, if 3-5% of handset manufacturer revenue goes on paying off the patents :( Separate to patents, I suspect there are also 'secret' constants (lookup tables for compression codes etc) which folks may attempt to copyright, a bit like the DVD CSS secrets...