T-Mobile's Unlimited Everything plan is $79.99 per month. That's same price as it is to have an EVO or an EPIC on Sprint, and it includes Unlimited calls to landlines.
T-Mobile has a 4G network now called HSPA+. They claim that it maxes out at 21 Mbps down, but in reality it's comparable to Sprin't 4G speeds. And Sprint's WiMax isn't "true 4G" either anyway.
T-Mobile's network coverage footprint may be less than AT&T's (their GSM rival), but it's more reliable in areas where both carriers have coverage. T-Mobile can roam on AT&T network, but you'll be stuck with EDGE data speeds while doing so.
I still think Sprint + Verizon's roaming agreement makes for a better coverage footprint, and add in the fact that you still get 3G speeds while roaming. And while you don't get access to Unlimited Any Mobile, Anytime calling while roaming, you can use thos landline minutes that barely anyone nowadays uses instead of paying a hefty per-minute charge. And I believe Nights, Weekends, and Unlimited Sprint mobile-to-mobile calling are still in effect while roaming.