My Belkin car-charger/FM broadcaster accessory always complained whenever I connected it that the accessory was incompatible with the phone service and did I want to enter “airplane mode”? Every damn time you plug it in, you have to dismiss the damn dialog. I should point out that the phone services worked fine when connected, so I have no idea what prompted the dialog.
Up through beta 3 of OS 3.0 this trend continued, however as of beta 4 I have not seen the dialog yet! I hope with the attention of new accessory-specific APIs that some of the accessory actions have been reviewed and fixed.
Also, my Logitech “Pure-Fi” alarm-clock radio with iphone dock used to work fine by playing ipod music when the alarm goes off, however beta 3 was very unreliable. I noticed that beta 4 seems to be working with it again.