# Detecting SMS service status
**URL:** https://forum.sierrawireless.com/t/detecting-sms-service-status/4343
**Category:** Open AT
**Created:** [April 7, 2010, 9:38am UTC](https://forum.sierrawireless.com/t/detecting-sms-service-status/4343 "2010-04-07T09:38:33Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@JohnnySoft](https://forum.sierrawireless.com/u/JohnnySoft)
#### Post date: [April 7, 2010, 9:38am UTC](https://forum.sierrawireless.com/t/detecting-sms-service-status/4343/1 "2010-04-07T09:38:33Z")
Does anyone know if there is a way to verify that the SMS service is available - ideally before trying to send an SMS and getting an error code? Presumably theres an AT command to query the status of the modem, but where do I start looking ?
Basically I want my app to be able to recognise and reject a duff SIM card at start up. I check the initialisation state of the SIM but that always returns OK even with a bad SIM. Presumably that just means that the SIM data has been read out OK.
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### Author:  [@awneil](https://forum.sierrawireless.com/u/awneil)
#### Post date: [April 7, 2010, 10:24am UTC](https://forum.sierrawireless.com/t/detecting-sms-service-status/4343/2 "2010-04-07T10:24:23Z")
> [@JohnnySoft](#):
>
> Does anyone know if there is a way to verify that the SMS service is available
There is no specific way to check for SMS service.
You can check GSM registration with AT+CREG and/or monitor +CREG: and/or +WIND: unsolicited responses - clearly, you can’t do anything network-realted when you’re not registered to the network!
[forum.sierrawireless.com/viewtop … =15#p17708](http://forum.sierrawireless.com/viewtopic.php?f=7&t=3766&hilit=faq+wiki&start=15#p17708)
You could also check that AT+CSCA does not give “error”.
> [@](#):
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> ideally before trying to send an SMS and getting an error code?
When you do get an error code, be sure to check it to see if it indicates a network problem!
> [@](#):
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> Presumably theres an AT command to query the status of the modem, but where do I start looking ?
Why, the AT Commands Manual, of course! 8)
> [@](#):
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> I check the initialisation state of the SIM
How, exactly, do you check that?
> [@](#):
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> but that always returns OK even with a bad SIM.
What, precisely, do you mean by a “bad” SIM here?
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### Author:  [@awneil](https://forum.sierrawireless.com/u/awneil)
#### Post date: [April 7, 2010, 10:35am UTC](https://forum.sierrawireless.com/t/detecting-sms-service-status/4343/3 "2010-04-07T10:35:08Z")
> [@awneil](#):
>
> monitor +CREG: and/or +WIND: unsolicited responses
Note that +WIND: 16 is documented as,
> [@](#):
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> SMS and SMS CB services are initialized
This refers only to internal initialisations within the modem - you also have to wait for network registration.
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### Author:  [@JohnnySoft](https://forum.sierrawireless.com/u/JohnnySoft)
#### Post date: [April 14, 2010, 11:08am UTC](https://forum.sierrawireless.com/t/detecting-sms-service-status/4343/4 "2010-04-14T11:08:34Z")
Thanks again awneil, very helpful as always. The bad SIM I referred to was such that the modem was unable to register on the network and my software didn’t detect that. I got the SIM initialisation status OK, but I think that just means that OpenAT has managed to read the SIM data.
In the end I used the response to the CREG command to determine network status. More useful to my app and not necessarily just to do with the SIM really, could be a variety of reasons.
Thanks.
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### Author:  [@awneil](https://forum.sierrawireless.com/u/awneil)
#### Post date: [April 14, 2010, 1:13pm UTC](https://forum.sierrawireless.com/t/detecting-sms-service-status/4343/5 "2010-04-14T13:13:04Z")
> [@JohnnySoft](#):
>
> I got the SIM initialisation status OK, but I think that just means that OpenAT has managed to read the SIM data.
Correct.
SIM initialisation is necessary, but not sufficient.
> [@](#):
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> In the end I used the response to the CREG command to determine network status.
CREG state = 1 or 5 is necessary and sufficient.