Voicemail? - did you travel ouside the US at all ?
last week while in the UK - received the following text message once I got signal :
"T-Mobile welcomes you to the UK! You may earn Hilton Honors bonus points or MilleMiglia miles whilst roaming our network. Visit www.travellingconnect.com
also received a few other text messages depending what network I roamed to - such as o2 or orange..
So why you'd get an oversea's call - if you hadn't been roaming - is very strange indeed..