I doubt it's the filters, mine have been working fine for over 2 years. I also doubt that all of the filters would go at the same time. Usually static changes while DSL noise is steady. Static will come and go or be louder at times and softer at other times. DSL noise is steady, it doesn't change volume and doesn't come and go. Does the static get worse when it's damp out, when it rains or when you have a wet snow? If that's the case then the problem is almost certainly in the lines between SBC and you.
Is your DSL affected? If I take my filters out not only do I hear DSL noise on the line but my DSL speed becomes horrible, barely faster than dial-up. I had bad static on my line at one time but it didn't bother the DSL at all.
If you know where your network interface (NI) is, around here it's usually on the back wall of the house, you can take a phone you know works properly and a DSL filter and plug in at the NI. Open the cover on the NI and you'll see your house wiring plugged into a normal looking phone jack. Unplug that and plug the DSL filter in it's place and then plug the phone into the DSL filter. If you hear the static there it's SBC's problem. If you want to try a new DSL filter they cost a few bucks at Radio Shack or Best Buy.
Since all your phones have the same problem the most likely cause is a bad line protection device - the protector(s) are inside the demarc box (demarcation - where your inside the house wiring connects to the phone company's wiring). From the sound of it you probably have carbon-based protectors - over time they can become noisy and need to be replaced. Or you could have a new gas-based protector - these fail a lot less but I have had one of these go bad too. Either way you should have the phone company come out and look at it...
One possibility is moisture in old lead-cased feeder cables. It's a common occurance this time of year. Squirrels gnaw holes the lead casing, allowing moisture to enter and contaminate the paper-insulated copper pairs. The first sign of moisture contamination is excessive static. If enough moisture gets in, the resulting leaking current is enough to create an off-hook condition. Callers receive a busy signal. The subsriber gets a dead line.