I've used the SIM340 module. It seems to work but we've found the support from the Chinese source mediocre. The manual is also poorly written and there are a number of pins that are barely documented in the manual--and that bit the designer of the board in the project.

I've also used a modem from Multitech. It, too, mostly works. But we got an unacceptable number of "CME errors" that weren't documented other than an unhelpful 1-line description in the manual. The manufacturer of the modem couldn't explain what the errors meant beyond that useless 1-line description.

The common theme here is that documentation and support for GSM modems seems to be consistently bad.

Regards,
Craig Steiner