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New PAYG SIM in Siemens TC35 GSM Modem problem

2: Seeker



I have been using an EE SIM (was originally T-Mobile) with a Siemens TC35 Modem for around 5 years now and I have never experienced any isseus.  However I now wish to use a Vodafone SIM and ordered a free PAYG one which arrived promptly.  The new SIM however fails to register on the network when used in the TC35 but will work in a phone.  I have activated the SIM, put credit on it and also made a few voice calls with the phone no problem, still wont register on the network in the TC35.  I spoke to Vodafone on the online chat who couldn't help but suggested I call 191.  I spoke with the Tech Support and explained my issue, the lady said she had updated the SIM and I was to turn off the phone, remove the battery and SIM, wait 3 minutes, then try it again.  I didn't hold out any hope when I tried it again in the Modem and sure enough, it failed to register.  I have gone on to the settings on the Vodafone account and disabled Data as I only wish to send SMS messages (I also don't require voice) via AT commands via the Modem, again no difference.  I have a number of other devices with Vodafone SIMs that all work great so I know its not a poor signal.  I reallt don't want to go back to the EE SIM so if anyone has any ideas it would be much appreciated.


Here's a link to the Modem I'm using:






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17: Community Champion

Hi @iamthelad


It could be a compatibility issue between the payg sim and payg settings and your router and or router settings. 

From what you say the sim card is working as it should because it works fine in a phone which is its primary reason for usage.

Be careful with using a Vodafone Payg SIM just for sending sms as they do have a fair usage policy and if a person exceeds those T&C then they've been known to suspend the sim card. 

Current Phone > Samsung Note9 _512Gb > Model: SM-N960 Duos.

Samsung Gear s3 Frontier Watch.

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Community Champion (Retired)

If it's a PAYG phone SIM, then check that you're using the correct APN - - see

On the other hand, it could be that your device requires a data SIM, but then things get complicated. Firstly, I think you'd have to go to a store to get one, but secondly, I don't believe that Vodafone's PAYG data SIMs will send SMS, although they can receive them; there's certainly nothing in the charging structure for outgoing SMS.

What sort of quantity of SMS, BTW? If it's just a few, you'd probably do best to run in straight PAYG mode, and pay 14p a throw. You could buy a Text Extra to give you 500 texts across 30 days, but relying on the unlimited texts in one of the larger Big Value Bundles could get you into problems with fair usage, as @BandOfBrothers mentions.

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2: Seeker

Hi @BandOf Brothers, thanks for the reply.


I will be sending under 100 SMS per month so think I'm okay on the fair usage policy but thanks for pointing it out. 


The Modem is GSM only, no GPRS or EDGE so wont pass "internet data" via the serial port, i.e. won't route internet traffic so I don't think the router or APN settings are applicable.


I'm beggining to wonder if the SIM is just not compatible with my intended usage.  The SIM is a free one with the spend capped at £1 per day, I wonder if it was a straight PAYG (i.e. 14p per SMS) I would get better results as @Annie_N has suggested?



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Community Champion (Retired)


It could be that PAYG1 isn't compatible with your intended use - it has only been around for a few weeks, so there isn't much of a track record - but that is easily fixed. Just text STOPPAYG1 to 40514, and that should put you into basic PAYG mode. If that does the trick, then for 100 SMS a month you might want to add the Texts Extra, which would automatically renew at the end of 30 days provided you had an adequate balance at the time, unless you opt out while it's running.

Please let us know how you get on! 

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2: Seeker



Thanks for the help guys.  @Annie_N I did switch to the normal PAYG tariff as you suggested but it again failed in the Modem.  I did however, manage to get hold of an identical Modem from a friend and tried that and it works so I can confirm that the "normal tariff PAYG" will work for my given application, hopefully that will help someone else who wishes to use a Vodafone SIM in a similar way in the future.  As it stands I am unable to confirm if the £1 per day fixed tariff will work but I don't see any reason why not.  I'm just glad I can finally get rid of my old EE SIM!





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