Most independent DSL providers are CLECs, which means that they also could provide voice telephone service if they really wanted to.

The catch for most CLECs right now is that while they may run their own wiring throughout a metropolitan area, usually the last mile is still hooked up to the friendly neighborhood monopoly (or former monopoly). In order to get their local (meaning metro-area) wiring connected to your house, they have to go into the monopoly's local CO and connect themselves to your individual line. (And, objectively, this makes some sense. How would you like to have six different telco boxes nailed to the outside of your house, with only one active based on which local telco you choose?)

This is why, despite the recent proliferation of CLECs (especially DSL-only providers) in the USA, a strike by the local monopoly (at the moment, Verizon) still paralyzes any modifications to the local telecom system. The CLECs are dependent on the monopoly, so they can't do jack until they can get into the buildings again and deal with people who know what's going on.