I just tried a United Mobile balance notification from Connecticut. Worked fine. Had to manually switch from T-Mobile to Cingular because in my area it will default to T-Mobile when both carriers are available. Probably just a system glitch in your area.
You may want to take along the landline number for United Mobile just in case the problem persists when you reach Europe:
If you require assistance of any kind, pleas contact our Customer Service.
Opening hours
Monday to Friday, 8.00 am to 6.00 pm (Central European Time)
Our service center is closed on official holidays.
Hotline
From your United Mobile phone dial: 094
From any other phone dial: +423 663 099 911
Online
Email:
customer.service@united-mobile.com
Phones/Wireless Devices: Doogee S90, Isatphone Pro, Amazon Kindle 3G, SkyRoam MiFi device, Karma MiFi device, AT&T Liberate MiFi device
Sim Cards: T-Mobile (Mint), AT&T (Mifi device or Kindle), Koko
Satphone: InMarSat
Broadband US Wireless Data: AT&T postpaid, Sprint (Karma Mobility prepaid)
Broadband International Data: SkyRoam
VOIP: Skype