...is to visit the manufacturers' support pages and seek out the online user manual for each particular model. It's often downloadable. My second choice would to use the wireless carrier's support pages & forums to see what they support on their approved devices. A backup would be to post questions as very specialized forums such as howardforums.com.
hope that helps,
I'm pretty new to cellphones and I'd like to get one that has good sound quality, has good play back features for music files, and one that I can use files for my ringtone and customize it, etc. I heard that some Sony, Nokia, and LG phones can have music files as the ring tone. How do I know which phones allow you to do that?