Carnt hear anything when ringing mobiles

This is a strange one!
When i ring mobiles i carnt hear the dial tone or the other person but on the screen the little phone is flashing saying its ringing and when the person picks up it comes up with the amount of mins and seconds, if i ring my house phone it works fine, im on t-mobile if that means anything and am not on the current new software as it says theres no updates still!!