Can I buy an UNLOCKED iphone 4 and use my Tmobile SIM card in that phone?

I wanted to know if i should buy a unlocked iphone 4 and use my android T mobile sim card in the iphone? Will it work? Or would i be wasting my money?
Also my phone is a GSM PHONE and the Iphone 4 is a GSM as well

Yes if the iphone is unlocked thats fine you can use any carrier… However, you may need to get it cut because of the different sim sizes this means buying a micro sim cutter of ebay or amazon for under a fiver

I don't see why not. SIMs are not mobile OS specific. They are just SIMs.

To help put it into perspective the same SIM I used in my iPhone 2G & 4 was originally bought before the iPhone existed.