We have SMS problems with the "new" type U-SIM card (KPN The Netherlands)
The problem is that with the U-SIM card SMS messages are not delivered to some trackers.
I tested Sanav GC-101, Sanav Webtrack 4-S and Intellitrac X1-pro both the GC-101 and the X1pro had these problems. The Webtrack 4-S was o.k. Changing to the "old" type SIM card solved the problem.