This trick, from an Amazon review by Theseus, makes the iTrip usable…
You can make this unit tune to 87.9 FM to broadcast. This is a “hidden” feature (a.k.a. Easter Egg) of the device. If you go into the settings menu under “Mode” you have the option to do Stereo/Mono on the right and to enable/disable “SmartSound” on the left. In the middle there is simply the logo for “Griffin” displayed on the screen. Normally it's at the bottom of the screen (bottom center). If you press and hold the center button under it for about 10 seconds, it will jump to the top-center position. This will open the transmitter up to transmit on frequencies less than 88.1 FM.
Why is this important? Legally, radio stations in the U.S. are restricted from broadcasting lower than 88.1 or so (there are exceptions), so it's almost always a fairly open frequency anywhere you go in the U.S. (not necessarily true in other countries). Most car radios can tune that low as well (for use in other countries).
I found that using that trick, the unit seems to be in a stronger broadcast mode. I'm not sure if it is a power boost or if it's just due to less interference from terrestrial radio. Either way, it's a huge improvement over the out-of-the-box settings but still barely average for an FM transmitter in my early testing so far. The AutoScan still doesn't work (in a semi-rural area with only a few moderately strong radio signals). The RDS doesn't work consistently. Still a huge disappointment vs. my Kensington.