First upgrade to .107 on your Pearl. http://www.blackberryforums.com/gene...2-1-107-a.html
Second you could have a 4GB card and that won't help at all. The card is for media not operational memory for the Pearl.
Unless you have a backup of the messages they are gone.
This is a known issue.
Also follow these tips: How do I free up memory on my device? - BlackBerryFAQ