If i cut my regular size SIM card will it work?

I have the iPhone 3GS and my brother upgraded so hes giving me his iPhone 4 which requires a smaller SIM card. If i cut the SIM card to the iPhone 4 shape will i have access to using my data? I've cut my other SIM card and tried it on a HTC One X and I had no access to data. So will I have access to my data?

Ring your carrier ask them to send you a sim that hits iPhone 4 with your old number on it. If you cut it yourself it won't work. And it's free