It's not always just about how many mili-amps the supply pushes! I've got a bare minimum/cheap 700mA phone charger running my Pi. I'm currently running maxed turbo, have in the past manually OC'd it up to 1000MHz, and have had NO issues yet.
Having said all that, the first phone charger i used (made by the exact same company, and same specs) gave me start up troubles.......I finally got out the trusty old volt meter and checked the Pi across TP1-TP2. #1 charger was only putting out 4.45V, #2 charger puts out 4.93V......do I need to tell you which one I kept??
Voltage matters!! (seems I've heard that about size also?)
If my former sig offended you I am sorry...it was a quote from Douglas Adams - HHGTTG