I'm working on a 3G modem board this week, based on SIM5320 (as suggested in a HackerNews comment, IIRC) - the way I'm designing it, it's pin-compatible with 2G modem I have now, so should be a drop-in replacement. Hope to have the PCBs in a month, and I'm also planning to release a timelapse of me drawing this board (with comments) - for educational value.