Like kate, I assume you mean sd card rather than SIM.
The only thing I'd add is that I'd not buy microSD cards from eBay. There are just too many people selling "fake" cards, i.e. small cards that have been hacked to look like large capacity cards to the phone, but will not be able to save significant amounts of data (will overwrite or corrupt files if you try). Best to stick to known and reputable suppliers for this.