Not wanting to fall into the same trap as OVMS v2, where the entire board is designed around the modem module, we designed the OVMS v3 system to have optional pluggable modem boards. We want to be able to exchange modem board, for newer technology, without having to change the entire system.
As you can see from the picture, we have modem boards working with both 3G and 4G chipsets. We designed the modem circuit board itself to support different modem modules, and our current modem board design supports both SIM5360 (3G) and SIM7100 (4G) modules, on the same board layout. The decision as to which to build (3G vs 4G) is made a production assembly time by soldering in the appropriate modem module.
However, today, the SIM5360 modules are almost six times the price of our old SIM900 ones, and the SIM7100 is almost twice that again. So, we can support 4G modems - but it is just too expensive at the moment to be worthwhile. We are also concerned because 4G LTE NB-IoT is coming soon, and that seems a much better match for what we require (SIM7000 module).
So, we have decided to stay with 3G for the moment, and see what happens with NB-IoT later this year (2018). We will then either release SIM7000 or SIM7100 modem option.