FrontlineSMS let users send, receive and manage SMS over a mobile network.


I am trying to use a ZTE MF620 modem with an AT&T goPhone SIM in the USA with the Windows (XP) version of FrontlineSMS 1.4.8.

In fact, this is the very same modem mentioned here by Sean.

When I run FrontlineSMS after having closed the ZTE app, the modem is recognized, the number is read properly, but it fails to connect. I get "SIM card invalid.: GSM network registration failed." It sounds like Sean was getting this problem in Indonesia as well.

Would anyone be able to identify under what circumstances that error occurs? Is the issue with the modem being locked to a specific provider (what this thread seems to suggest)? Is it with the device itself being blocked by providers?

Thanks very much for your help.


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Hi Hélène

Thanks for the message.

Where did you get the modem from? Is it an AT&T branded modem? I'm not 100% sure where the message is coming from, but if the modem is locked to a particular network and it's not AT&T then this might explain what's happening.

Does the SIM card work in a regular phone? It may be worth checking, just in case it's corrupt or faulty.

I'll leave the developers to respond if they have any other ideas - let us know if anything above helps or makes sense!


Hi Ken,

Thanks so much for your prompt response. =)

I should have provided a few more details. I tried two different AT&T gophone SIMS as well as a T-mobile one. All 3 work in phones but get the same error in Frontline.

The modem is Indosat branded, but I believe Sean got the same error with an Indosat SIM in Indonesia.

We suspect it's a modem issue that we probably can't get around, but it'd be great to have confirmation.



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