sprint vs GSM?

[orangekid]

I am on sprint and would be content to stay, but my friend is getting a new iphone and would sell me his 2G for really freaking cheap. I'm sure I could probably trade or sell/buy my CDMA diamond for a GSM diamond, so I'd have two phones, then if I signed a contract I could get a blackberry storm or some other phone, that way Id have 3 phones all for pretty cheap. But I like sprint, so I was wondering if someone with T mobil or ATT who has a comparable plan to mine could fill me in on price/reliability. Currently I do the unlimited data, unlimited txt, and 450 daytime mins with free nites and weekends that start at 7pm for $70 a month. Is there a comparable plan to this one GSM? Does anyone have a t mobil diamond and do they like it? any info is appreciated.