We are using a 2n Office route ( sip gsm gateway ) it has 2 sims at the moment ( but room for 4)on a CXII running MCD 5.0 SP1
Works pretty well most of the time , occasionally the 2n needs a reset.
We have also used analog Gatways before but the Sip ones work a bit quicker. ( call connection delay is less with SIp than with Analog)
If I never did anything I'd never done before , I'd never do anything.....