Yeah, read the second post in this thread.

It's really unfortunate that most decent after market headphones are now iPhone compatible rather than Nokia compatible - suspect Nokia need to get in line with Apple, as much as that may suck. Or bundle an Apple compliant adapter with every Nokia device, something like this (although designed to convert the Apple 3.5mm socket into a "Universal" [ie. Nokia] socket - most likely by swapping pins 3 and 4 - it should automatically work the other way when connected into a Universal socket by again swapping pins 3 and 4, right?).

Was thinking of getting an Ultimate Ears + Mic headset, but since they're iPhone compatible it would be a waste of time using them with an N900 (or any Nokia for that matter). Total nonsense.