Here's a comparison of features, Evo 4G vs iPhone 4
Advantage iPhone 4
----------------------
--Thickness: iPhone 9.3 mm; Evo 12.7 mm
--Weight: iPhone 4.8oz, Evo 6oz
--Dual microphones (noise cancellation): iPhone yes; Evo no
--Gyroscope (game play): iPhone yes, Evo no
--Built in Storage: iPhone 16GB/32GB, Evo 440MB (but SD card slot)
--Wifi: iPhone 802.11n, Evo 802/11a/b/g
-- App store: iPhone 200K, Evo (Android) 50K
Apple claims the battery life of the iPhone 4 has improved, and lasts longer than the Evo 4. We'll have to wait for the iPhone 4 to be tested to verify. If the battery is low, the Evo battery can be replaced with a freshly charged one. The battery in the iPhone can't be removed.
Advantage Evo 4G
----------------------
--Display size: iPhone 3.5 in.; Evo 4.3 in.
--Front camera: iPhone VGA; Evo 1.3 mp
--HDMI out: iPhone no; Evo yes
--Kickstand: iPhone no; Evo yes
--Free Navigation: iPhone no; Evo yes
--Video chat: iPhone Wi-Fi only; Evo Wi-fi/3G/4G
--Mobile broadband support: iPhone 3G; Evo 3G/4G (WiMAX in some areas)
--Flash support: iPhone no; Evo Flash lite yes
--Tethering: iPhone yes, extra AT&T charge, Evo yes, no extra charge
--Wireless Hotspot: iPhone no; Evo yes, Sprint extra charge
--Replaceable battery: iPhone no, Evo yes
--Slot for Flash memory card: iPhone no, Evo yes
--FM Radio: iPhone no, Evo yes
--Speaker volume: iPhone loud, Evo louder
The Evo is very large for a phone. For some people this is a deal-breaker. For others (myself included) a little more space on the screen will be welcome for text entry and dialing the phone.
Features common to both phones
----------------------
--HD video recording: iPhone yes; Evo yes
--Processor: iPhone 1GHz A4, Evo Snapdragon 1GHz
Not clear if this is an advantage one way or the other
----------------------
--Display resolution: iPhone 960×640; Evo 800×480
--Rear camera: iPhone 5 MP; Evo 8 MP
--OS: iPhone iOS 4; Evo Android 2.1
--Multitasking: iPhone limited; Evo full
--Carrier: iPhone AT&T; Evo Sprint
--OS updates: iPhone via iTunes; Evo OTA