The new model of UCM/GSM4 module which works on the 3G network is now available, model number UCM/GSM4(3G).
This is necessary in countries where the 2G network has been shut down, like Singapore and Australia, with other countries perhaps following suit in a few years
Even where the 2G network is available, there are several advantages to UCM/GSM4(3G).
Some 3G Sim card plans may actually be cheaper for network providers which do not support 2G
Dialing to Central Monitoring Stations via 3G GSM is reliable compared to 2G. 2G dial out to Central Monitoring stations does not work reliably over 2G GSM because of speed and delays over the network, but this is not a problem for 3G
Higher security for 3G over 2G because of encryption, reduced chances of impersonation.
The UCM/GSM4(3G) specs include Quad-Band GSM/GPRS/EDGE 850/900/1800/1900MHz which is 2G so if it is unable to get a 3G signal, it will fall back to 2G automatically
However you say the 3G signal may not be bad enough for a phone to switch to 2G, it is not able to force operation in 2G. In such situations, it is better to use the 2G model, since the location would be fixed.