Quite simply, if you don't use Google Voice yet, you are missing out.
Bonus: Cost. While retail prices of high-end Android devices are often as high or higher than the $199 AT&T plan currently offered for the Windows 7 series and the iPhone, third parties like Amazon and Wirefly bring costs down considerably.
Also, AT&T's plans are as expensive as any in the US. Sprint and T-Mobile often offer discounted monthly data plans which will, over the life of the phone, save consumers much more than the phone's price.