[inquisitor]

Have you tested different destinations? From my observation Dellmont (formerly known as Betmax) have a pretty dynamic routing which makes use of unused capacity from carriers around the world who sometimes don't present the caller ID you've set but instead none or one from their own network none (often from countries like Russia or China). Also I've seen calls to Eastern European mobile networks to be terminated through GSM gateways/SIM boxes (which is illegal). I don't say they deliberatly use such illegal methods but probably their wholesalers do.
That said these caller ID issue usually apply only to certain destinations and are only temporary.