FRIEND,if it is a post paid connection,u hould contact QTEL for transfer in ur mailing address,and then u can verify if there is any pending payment left for that no.
if it is a prepaid ,the question of out standing balance does not arrive,still we should approach qtel authorities to verify any legal/crminal issues pending in this no(regards personal).then after the certification frm authorities only u should change to ur address ,but still u will have personal problems when u use this no,many calls will b there asking for the previous owner and chance of sms also if he is subscribed to any facilities from govt service or banks .