Does anyone know of a website where I can find out exact guidelines for MTTR on T1 lines and DSL/cable lines?

Don't know if this is what you need, but try it.
http://www.leasenet.net/php_main.php?id2=products&id3=internet

http://www.commsdesign.com/design_center/g3wireless/design_corner/showArticle.jhtml?articleID=16505032