AFAIK, depending on IOS version, the max-paths you can load balance with
CEF is 6 or 8. i.e. In some older versions, it is 6, and I've had to do
upgrades to get 8 T1's to load share.
Most instances of this that I've done have been on our own network where
we use OSPF on the T1's and set maximum-paths in router ospf. I have
seen/done 4xT1 service load balanced to customers using static routes.