U-Verse phone is actually VoIP, so there's likely not much you can do, other than see if AT&T has some special settings they can apply to your line. Call them and tell them you're having trouble with an alarm system or a fax line and see if they can help. It's not going to be a DSL filter problem.
2xTiVo Premiere on Charter Digital Cable
Former: S1, S2 TiVos, Microsoft UltimateTV, 3 SD DirecTiVos, SciAtl 8300HD (Pioneer), DirecTV HD DVR (HR-2x), DISH 722k, TiVo HD