SM5100B GSM shield + arduino power supply inquiry

I am working in a project that involves using GSM shield and arduino UNO, I am using the sparkfun GSM shield SM5100B http://www.sparkfun.com/products/9607
, and I am using arduino UNO.
I read that during communication bursts , the current should be 2A therefore an external power supply should be used. I thought of using an external (5V,2A) AC adaptor connected to the arduino, but I am not sure that is the right and the safe solution ?? I read in some blog, not to use adaptors, without mentioning a reason. I want to know if this is a working solution and a safe one ? and if there are any alternatives?

I read in some blog, not to use adaptors, without mentioning a reason.

If you are going to believe that, what could we say here that will make you change your mind?