CellularInsights was a source. My undergrad is EE/CS and I studied digital comms as well as meet Qualcomm people mobile health summit and other health computer conferences.

Sources included iFixit which discussed the chips involved (but neglected to mention whether there were 2 or 4 antennas in iPhone 7 which cellular insights did provide), Qualcomm data sheets, Tmobile and Verizon press releases, fiercewireless, howardforums, Enhanced Voice Services (EVS) specs and datasheets from Ericcson, Nokia, and others.