Here is a tip I posted on Howard Forums:

For those who own the 6265i, I strongly suggest you get the stereo headphone adapter kit for the Slider Remix.

First of all, you can get FM stereo to work through the headset. Simply find a way to plug-in the Nokia-branded headphone adapter which plugs into the bottom of the handset. Start the FM radio, and then plug-in the headset in the standard headset jack on the side.

From now on, you will be able to start the FM radio as long as the headset is plugged-in.

The headphone adapter for the Slider Remix works perfectly well with the 6265i! You get full stereo sound, and the unit's microphone works, too. It adapts the headset jack to a standard 3.5mm headphone jack. The nice thing is you can use ANY 3.5mm headphones/speakers/adapters/etc. with the Remix'es headphone adapter. I use my FM stereo adapter ($30 bucks at Wal-Mart) to answer calls hands-free and listen to my MP3 playlist through my car's in-dash FM radio!

The music controls only advance or reverse a radio station or song track, but they DO work. The play/pause button also works, but it only advances forward. You can't answer the phone using the play/pause button, either. The volume buttons do not function at all.