oscarsthegrouch:
Any ideas on how i would go about choosing the correct sensors etc to use with an Arduino would be greatly appreciated.
Just a piece of general advice...
Initially, you should have a very clear concept of how exactly you want this grid to react to the cell phone transmissions. For instance, a grid that just turns on when it detects one or more cell phone signals is going to need much less sophisticated sensoring capabilities than one that can vary the color or brightness of small patches of LEDs based the activity of nearby phones. Once you have a better handle on your design requirements then you'll be in a better position to start evaluating specific sensor options.