Call orginated from Asterisk goes to mobile voicemail


I am facing an inconsistent behavior with Asterisk 1.2.4 with VoIPJet on outbound calls to mobile phones. For some of the outbound calls, they will go the the mobile phones’ voicemail directly even the user didn’t press any key. The correct behavior should be to make the mobile phone ring.

Anyone faced this before or has some ideas what could be wrong?