The Cisco endorses 3845s for T3s, seen here: http://www.cisco.com/en/US/products/ps5855/prod_models_comparison.html. My experience has been the 3845 works very well for most T3s, but the 3825, although only recommended for half T3s in the prior link, seems to work very well for most T3s also.
PS:
Any router than can provide 200 Kpps or more forwarding performance seems to often work well with T3s. See attachment for pps ratings of various Cisco routers.
FYI...I'm using a Cisco 2811 with the NM-T3 module and doing fractional T3 speed of 22 megabit.
It works fine!
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