1) CDMA has a standard for something similar to SIM cards that is used in places outside of the US. Verizon never wanted it though, and the phone companies build what the carriers want, not what consumers want.
2) LTE is compatible with both CDMA and GSM, and furthermore specifies a SIM card. All my recent Sprint phones have SIM cards that is used solely for CDMA
3) I expect the Sprint CDMA network is more valuable than the T-Mobile GSM network, but my information is out of date; if T-Mobile has been buying up spectrum faster than Sprint, they may have caught up.
4) T-Mobile actually owns some CDMA spectrum as a legacy from MetroPCS
5) For at least a couple years after the merger, I expect that both 3G networks will continue to operate; it's possible that phones specifically for rural areas (which will get LTE last) with the ability to connect to both will be made; IIRC T-Mobile sells some tri-band phones that connect to bands it owns no spectrum in specifically for allowing that (though it's still GSM, not CDMA).
2) LTE is compatible with both CDMA and GSM, and furthermore specifies a SIM card. All my recent Sprint phones have SIM cards that is used solely for CDMA
3) I expect the Sprint CDMA network is more valuable than the T-Mobile GSM network, but my information is out of date; if T-Mobile has been buying up spectrum faster than Sprint, they may have caught up.
4) T-Mobile actually owns some CDMA spectrum as a legacy from MetroPCS
5) For at least a couple years after the merger, I expect that both 3G networks will continue to operate; it's possible that phones specifically for rural areas (which will get LTE last) with the ability to connect to both will be made; IIRC T-Mobile sells some tri-band phones that connect to bands it owns no spectrum in specifically for allowing that (though it's still GSM, not CDMA).