Can i use any sim in an iphone 3gs?

Been giving an iphone 3gs. Just wondering if i could use my Standard sim in the phone? And on my current plan i get unlimited internet, would i still be able to use the internet or do i need 3g? Apparently i can't use imessage with just internet is this true or yet again do i need 3g?

Sometimes but its more likely youll need to get it swapped.

Also i don't know who told you that about imessage. You can use it with any form of internet (Wi-Fi or 3g)