Ambrosia has released iToner 1.0.3 today, which supports the iPhone 1.1.1 revision.
iToner allows you to transfer MP3 or AAC files to your iPhone for use as custom ringtones. Unlike Apple's solution, this lets you use your songs without an additional per-song charge.
Apple's last iPhone 1.1.1 update broke compatibility with previous versions of iToner, but the 1.0.3 update fixes this incompatibility. iToner sells for $15.00, with a fully functional trial available.