iPhone 4 calls going directly to voicemail

[jonjonjonjon]

When I'm inside of any app, Camera, games or whatever any incoming calls doesn't ring, they just go directly to voicemail and later I receive the SMS telling me of the missed calls, the calls only pass through well the iPhone is without using any app or some seconds later after I exit the app in use, please somebody help!

I'm using iPhone 4 iOS4.0.1 jailbroken with jailbreakme and unlocked with ultrasn0w

[Waleed786]

What service provider?

[jonjonjonjon]

Movistar, a venezuelan provider, but this didn't happen with my 3GS