Dear Drama Queen. Thanks for the update. It is most unlikely, that a TMO Simcard is roaming on A1 since they are competitors and there is definately NO national roaming agreement in place between A1 and TMO.
More likely is, that your vectone mobile is allowed to roam on A1 since this has been the original provider for vectone before they moved to TMO just recently.
If you want a service that uses A1 network, there is a wide choice:
- BOB
www.bob.at
- YESSS
www.yesss.at (only available at Hofer ((Aldi)))
- BilliTel
www.billitel.at
- Ge-Org
www.georg.at (MVNO brand of Media Markt)
- B-Free
http://www.a1.net/handys-telefonie/bfree-wertkate-plus (original prepaid by A1)
All of them offer good services including data packages a certain prices, however B-Free seems to be the most expensive one. For low priced international calls you should have a look at BilliTel.
All the best...
BK
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Mobiles: iPhone 7+, iPhone 7, iPhone SE, Blackberry Priv, Honor 8, Lumia 950
Prepaid-SIM: 3 UK, Save Money Sim, Toggle Mobile UK, XX-Sim, Koko Mobile