It is possible to upload iTunes mobile client to a SLVR L7 that is not through cingular. You can even hack the iTunes Software to allow up to 1,000 songs. If a thing is called software, then that thing can be hacked....
www.slvrfiles.info
you have to register with the site before you can start downloading the necessary software to make itunes work on your phone. Also, in order to do this, you need to use a Windows based computer, unless you want to spend hours at your computer ripping your hair out using Moto4lin (the apple version of P2K and motomidman.)
You will also have to do a search on google for a program called RSD Lite v2.5 (the program cingular uses to to flash it's phones and install iTunes on the phone.) You will not be able to find it unless you do a search on Google for "Cybermania."
From SLVRFILES you will be able to download a few different versions of iTunes, you can get iTunes in an all black skin, all red skin, and of course the original. If you want, you can even download the software that will hack the 100 song limit and make it to a 1,000 song limit.
have fun pulling your hair out because it's not as simple as it sounds...