This week I purchased an Audiovox SMT 5600 aka C500 and switched my cell phone service from T-Mobile to AT&T Wireless in order to get this phone, as I have been waiting for this combination of features and form factor in a smartphone for 2 years.
I was excited to try out synching some TV content between WMP 10 and my Media Center PC at home, so I ordered this 512MB Mobile Mini Secure Digital Card from ECost.com. I wanted to be very careful that I got a mini-SD and not an SD, but as you can see, the title of the item clearly says Mini. The description says it's compatible with SD slots, but that is to be expected as most mini-SDs sell sleeves so they also fit into SD slots.
I paid extra for quick saturday-delivery shipping and when it arrived this morning, I opened it only to see... a 512MB secure digital card. It doesn't even look like the picture on ecost's site - there's no "Mini" on the SD card itself.
If you look at epmemory.com, you will not see the same picture on ecost that has 'mini' on the card itself. But in the title of their main page, it appears that their line of products is all called 'mobile mini', they have "mobile mini" compact flashes for example.
I called ECost to get an RMA so I could return it, and the customer representative told me she knew exactly what the problem was, so I assume that I am not the only one who's made this mistake. So I'm out the money I paid for shipping it to me, as well as the money I'll pay to ship it back to ecost. Lesson learned.
I also called a few brick and mortars in my area this morning to see if they had any. One of them told me that oh yes, they had a 1 gigabyte mini-SD card for $109. "Mini? You're sure it's mini?" I asked. I was assured that it was. Somehow, I don't think so.
So if anyone else is in the same situation and looking for a mini-SD, be cautious that you're getting what you want. I'm heading out to Fry's later today, they have 256mb Sandisk mini-SDs in stock, I'll just have to cool my heels until 512s and 1gbs are available locally.
 Thus far, I highly recommend it. Especially if you're a new customer and work for a company that has an arrangement with AT&T, I got the phone for a very reasonable price.
[Update 10/18: Toshiba 512 MB Mini-SD for $109. Thanks, Steve!]