EIGRP has a limit of six parralel paths. If I use multilink on 6 T1 lines will that be one path. Could I use in theory 36 T1 lines? Any advice would be appreciated. I currently have a T3 in place that averages 10MB of utilization and want to re3duce costs by getting rid of the T3.
In theory you should be able to have 6 multilinks with 6 T1s in each multilink bundle. There would be some cost to provide the number of T1 interfaces that you are talking about. And there would be some additional overhead on the router to manage the links within each multilink bundle and some overhead to manage the 6 paths as compared to managing a single path. But I believe that is could be done.
I wonder if a more cost effective solution might be to ask your provider about a partial rate T3. If you do not need the full rate T3 then what would they charge for 10MB (or 15MB to give yourself a bit of room to grow)?