I bought an 8 gig micro SD memory card at Walgreen's this past weekend that was on sale for $9.99, marked down from $29.99. You remove the back cover and there's a little slot the card fits into. Make sure you turn the phone off before you do this. Once you've installed the card and turn the phone back on it automatically creates the same file folders on the memory card, that are on the simm card.
WARNING! Don't do what I did - Instead of installing the card in the phone first, I put the card in my computer and made my own directories, and for reasons unknown to me, that created problems. I wasn't able to copy more than a dozen files to the memory card, and later when I tried to delete the directories and the mp3's I downloaded from the computer, they kept reappearing. I ended up taking the memory card back and exchanging it, and the 2nd time I installed it in the phone, then connected the phone to my computer, and had no problems at all.