Not having usb cables now a days is like not having a remote for your tv, it's just such a convenience especially for someone such as yourself who likes to upload wallpapers and ringers. As far a breaking rules with Sprint there's no worries there unless you write them a letter stating all the modifications you've done with your phone.
Another convenience of having a usb cable is that you can used your phone to access the internet.
Get yourself a usb cable and have fun with your phone....
