[iPhone] Set custom ringtone with longer duration than Apple's limit

iTunes allows you to upload custom ringtones to your iPhone only if their duration is less than 30 seconds. An easy way to circumvent that limitation, without jailbreaking the device, is to trick iTunes itself.

Begin with following the standard procedure to add a valid song (any .m4r shorter than the duration limit) to your Tones library, but be sure to name it exactly as the ringtone you really want to add. Follow all the steps but stop BEFORE syncing with the device.

Now create a .m4r version of the ringtone you actually want (from iTunes, create AAC version, then manually rename it to .m4r) and save it somewhere. From the filesystem explorer, browse to the folder containing the short ringtone and rename it .bak (or whatever), then copy the full length version in that same folder; make sure that the two files are named the same way, except for the .bak extension.

Finally, you can start syncing. iTunes will load the full length ringtone instead of the short one, and will not complain about it.