iPhone 3GS on HSPA Network?

[Midknightkruzer]

[FONT=arial, helvetica, clean, sans-serif] I am thinking about buying my bud's iPhone 3GS to use on my current mobile phone carrier. I would then unlock it to use with my carrier. While doing some research I heard that only GSM networks can be used on unlocked iPhone 3GS. The company I am with, Solo Mobility, uses the HSPA network (Or at least that's what I have read). I already know my phone has a Sim card. So theoretically, I should just be able to pop out my SIM card from my current phone, and then insert it into the iPhone and everything will work, right? Or is my sim card not compatible? Help is greatly appreciated. Thanks in advance.[/FONT]

[FONT=arial, helvetica, clean, sans-serif] Also, sorry if this is the wrong section I am new here.[/FONT]