LittleL
For a compatible way to convert songs for SonyEricsson phones, I suggest using
SonyEricsson Media Manager. (free standard version:
here)
This software can convert Flac, Ogg, Wma files to AAC. I has been using it with W880i, it works very well, though kind of slow on starting up program. I do not know whether W810i is supported but I guess it doesn't hurt trying.
However, an annoying problem (for me) is this software does not allow you to edit tag nor it copies tag info from Flac files. You have to manually edit tag for those AAC files with another software, like,
Mp3tag.
In case you do not know this yet, some SonyEricsson phones have trouble arranging music files if double digit is used in "TRACKNUMBER" field, for example "01", "02". The best way is to use single digit; "1", "2" for "TRACKNUMBER". Also, do not put totaltracknumber in, SonyEricsson phones cannot read it. Something like "1/12", "2/12" will make your song sorted in wrong order.
For all SonyEricsson phones,
official guideline (@page 26) says they only support AAC-LC up to 192 kbps.
In my opinion, it's an overkill to encode songs at AAC 320 kbps anyway. Perceptible differences wouldn't present at that high bitrate.
[edit]
Since your phone also support HE-AAC v1, I suggest using it. HE-AAC v1 at 64-96 kbps give very good results. On my personal test, I cannot distinguish between HE-AAC v1 @80 kbps and original Flac file.