how come the Huawei HG659 VOIP functions wont work with Bigpipe yet my fritzbox 7360 does ? 

i think my fritzbox is on the way out(frequent disconnects) but my only other modem to test my line with is a Huawei HG659 (vodafone flashed to bigpipe firmware) , but ive never been able to get it to work (maybe im doing something wrong)

anyone specifically on VDSL ever got theirs to work ?