You can put an AT&T SIM in a T-Mobile phone; you just won't get 3G.

Also, unless the service plan cost is a complete dealbreaker, which I can certainly understand, you can still get a 30-day trial from Sprint.

My N1 generally makes it a full day unless I have particularly heavy usage, and, even then, generally charging it in the car on the drive to wherever is enough to top it off for the day. It also claims, in almost all cases, that a definitive majority of the battery is being used by the display, if you're to believe the report. So maybe there's some backlight tweaking to be done on the Evo.

(Also, it's spelled "idyll". Good word, though.)