To expand on the other already good answers here: 4x 1Mbps DLS lines != 4Mbps of throughput, it doesn't matter what load balancer you put in place. Unless the ISP is in the loop and is bonding the links together on their end to act as a single trunk, any single download stream is going to be limited to a single DSL line and capped at 1Mbps; you can't load balance an single incoming stream, say a large file from a web server, across multiple incoming connections. You can send traffic out multiple connections with the same destination, and you can receive in total 4 independent 1Mbps streams.
Unless the phone company is bonding the links on their end, you're going to have 4 IP addresses, which means 4 different point to point connections capped at 1Mbps. Multiple connections and Load balancing are good when there are multiple end points on each end of a connection, but your point-to-point speeds are limited by the fastest/slowest single link. When its 1-to-many (you-to-AllOfTheInternet) its not really doing you any favors except redundancy (though if all the links are from the same provider if one goes down, chances are so are all the rest, so nix that idea).
Also, $220/mo for a T1? for 1.5Mbps? Really? SLA or not, that is an outrageous amount of your income being flushed away into an overpriced business expense, especially when you're willing to take DSL lines (regardless of quantity or quality) as an alternative.
And just to top this off, it may sound prude-ish, but for future reference: When your job / way-of-life depends on having quality internet, that should probably be more of a factor in your home purchasing/renting decisions.