In your post, it says all 4 T1's will be plug into a switch? Do you mean ATT will give you 4 different routers? T1's cannot go into the switch (except 6500's with WAN module).
Assuming you have 4 routers, and since you didn't specify what version of software you are running, I am using ASA software v8.0 as a reference.
From the configuration guide of v8.0
You can define up to three equal cost routes to the same destination per interface. ECMP is not supported across multiple interfaces. With ECMP, the traffic is not necessarily divided evenly between the routes; traffic is distributed among the specified gateways based on an algorithm that hashes the source and destination IP addresses.
The following example shows static routes that are equal cost routes that direct traffic to three different gateways on the outside interface. The security appliance distributes the traffic among the specified gateways.
hostname(config)# route outside 10.10.10.0 255.255.255.0 192.168.1.1
hostname(config)# route outside 10.10.10.0 255.255.255.0 192.168.1.2
hostname(config)# route outside 10.10.10.0 255.255.255.0 192.168.1.3
HTH,
jerry