according to reviewers who have used it, the w760i is capable of 8GB
Quote:
“Sony Ericsson W760i Review
Reviewed by Grant from UK on 9th Sep 2008
ive just got this phone its great, enione tht says its not it is and it takes an 8gb card as im using one now and its fine, all the functions are amazing and work perfectly the phone wualits is good and the battery life is awsome lasts for ever and also looks slick lol, fast menu's and no crashing or white screens etc 100% perfect reccomend buy if you like walkman phones as i do ive had 3 and this is the best so far, speakers are also v.good and are very loud and clear no rattling or crackling.
Rating: ***** Outstanding”
link
so you should be okay, cubby
it may be that Sony says 4gb, only because that was the largest capacity available at time of writing.
(eg when the k800i came out 2 years ago, Sony said the maximum for that was 2gb, which is not actually true, but was true at the time only because 2gb was the largest card available then.)