ITunes locks out other devices by limiting synchronization only to iPods and other Apple-approved devices. There are third-party software you can use to be able to manage songs in your phone or non-iPod mp3 player using iTunes but these applications can be complicated to install or tedious to use.
I’ve long stayed away from using iTunes to manage songs in my Sony Ericsson K750i because I do not like the way it organizes files in the phone’s memory card. I also do not like the way iTunes locks out other players. For a long time, I’ve been using MediaMonkey to manage songs in my phone.
Still, at the back of my mind and figuring consistently in my to-do list, I’ve always wanted to try using the open source media player Songbird with my K750i. But for a long time, the “developer preview” label on the Songbird download link put me off from trying it. That label gives an impression of being unstable that only developers should try using it.