Being close to China, the motherland of x-sim, y-sim......z-sim, I have the chance to test out different sim solutions, so far, none of them work perfect all the time.

Problems I noticed were:
1) drop signal when working into poor signal area.
2) Cannot work with some 3G network (no service ) or 1/5 signal strength of 2G only( disable the 3 G network on the iphone) China does not has 3G network yet. Hong Kong has.
3) Roaming sometimes failed to register.

To me, it seemed that thesim solution is network dependent or even simcard dependent.

I still need to find a perfect sim solution that work as good as the old sim solution as in 2G iphone before.

Using 2G only is Ok for me as the 3G network I used in Hong Kong is worst than the 2G network. May be due to less repeating signal stations installed. I used 3G network & switch back to 2G network because of poor 3G network.

Is the sim solutions you are using has problems from time to time?