power supply for 5100b shield

it is clearly stated that the 5100b can require up to 2A for various functions to work. so an external power supply is required. Several places online say to run 5V @2amp power supply INTO the 5v pin.

I'm a noob and have always used the 5v as a power source(OUT) for various sensors etc.

Can you run 5v INTO the 5v pin and use it for external power for the board? I just want to be sure before I let out all the magic pixie dust on my board!

yes no?

I think it depends on which Arduino you are using. Look for "Power" at the respective Webpage....like: For the Uno Rev3 http://arduino.cc/en/Main/arduinoBoardUno it says:

5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

So NO. For the Nano http://arduino.cc/en/Main/ArduinoBoardNano it say:

The Arduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source.

So YES.

But, Here they say to do it....that's the confusion I'm having

http://tronixstuff.wordpress.com/2011/01/19/tutorial-arduino-and-gsm-cellular-part-one/

They (Tutorial) say:

Ignore this at your own risk. When connecting this supply DO NOT use the DC socket on the Arduino. Instead, connect the 5V (positive) from the supply to the 5V pin on the GSM shield, and the negative to the GND pin.

I think the arduino guys wouldn't write not to risk it if there weren't a possibility of damaging your Arduino. So either you just go with the tutorial (It worked for them) or to make sure look at the respective Arduino schematic and look why it might not go wrong with your Setup (I can't help you with that).

Someone else please pitch in to help redruff.

You need to do it. I simplified the tutorial to use a "power shield" that helps you out.