Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420.1 (KHTML, like Gecko) Version/3.0 Mobile/3B48a Safari/419.3)
If you have wi-fi you can access your email and the type of sim card is immaterial. Without wi-fi coverage I don't believe you can access email with an O2 PAYG sim, but I may be wrong about that.