For the cost of one of those T1 lines, you ought to be able to hook up about four (or more) of the DSL lines. Figure 3mb/s each, that's 12mb/sec -- quite an improvement over the T1 they replace, and you've still got the other (reliable) T1 there too.

MLPPP (multi-link PPP) is one possible way to "bond" the DSL lines, if the ISP can support it on their end. Otherwise a Linux box doing round-robin (or even smarter) routing can spread the bandwidth around.

Cheers