Im Having Problems Recieving Texts on Samsung Rant
If you haven't already, get a file management app from the marketplace that will allow you to move everything possible to the memory card. Upgrade your memory card if you need to. This should help some. Clear out the cache on your apps (FB is one of the worst for cache storing), and try the watchdog app. Watchdog will let you know what is sucking your processor dry or is sucking up more juice than it should be. That should help with memory issues and the slow phone.
I have noticed sporadic issues with texting on all 6 of our phones (laggy texts - as opposed to my friends with Verizon). I believe this is a Sprint network issue, not the phones. Luckily, it hasn't been bad enough in my area to be more than a nuisance. If I need an immediate response I call. I have found that all our phones have been dropping out of 3G (which means no service at all for 3 out of 6 phones). However, by turning them off and turning them back on it resets and we have service again. I have no clue why this works, but for now it does. HTHs.