have you tried using any programs that have easy and quick ways to free up some ram? for example, sk tools has that plus many options which may speed up certain aspects of your phone. quick menu has its 'hibernate' function to free up a couple megs of ram easily. QM also works as a reliable replacement for any task manager bc it really does close programs- and allows exceptions if some progs are desired to stay open. i try to soft reset at least once a day also, i think this just keeps the phone running better and keeps the ram above average.
regarding opening office documents, if you go here
http://www.microsoft.com/windowsmobi...icemobile.mspx you should be able to download the 2007 format to your phone and therfore be able to open all microsoft sorts of word, excel and ppt files.
your other problems do seem (to me) like they are only related to your specific phone. maybe sprint would be willing to get a replacement out to you?