reply to BF69
Re: Greed!!! Yes they do use different frequencies but they do have roaming agreements and the ability to roam on the other carrier if need be especially in Sprint's case. The phone should work on the other carrier because of that fact and the reason why carriers won't allow it is that they want you to buy a new phone with them. Mo' money mo' money...
Case in point, I was with Sprint and have a EVO 3D. Took the EVO 3D to Cricket and they flashed it to their network. It works just fine: 3G, MMS, SMS, so on. Matter of fact, the phone works better than when I was with Sprint! It doesn't randomly reboot or crash anymore and the battery life is worlds better. The only thing that doesn't work is WiMax, which is to be expected.
I get great coverage for my area with Cricket and the 3G speeds have been great, sometimes 2Mbps+. At $55/month for unlimited talk, text, and data, you can't beat it. We have saved ourselves hundreds of dollars a year just going prepaid. Plus it feels good not being tied down to a 2yr. contract with exorbitant ETF's!!