Would that prevent the system from working? I really like the feature set of the TI. I looked at the datasheet for the Sparkfun GSM module:
and it does regulate the 5V input to the GSM module voltage to ~3-4V.
Alternatively, could I employ a setup like this:
Use an adafruit lipo charger which has a direct battery output connection (http://www.adafruit.com/products/280) and boost that to 5V to power the GSM.
I would then power the Arduino via the 'DC out' pin on the lipo charger.
HOWEVER, what happens when I have this unit plugged into the wall and the GSM draws 2A? Is it drawing from the battery or from the charger IC? Doesnt that exceed the IC current? If drawing from the battery, wouldn't that deplete my backup power supply?
With the TI module, all power comes from the wall source when plugged in, and battery when unplugged. It seems like a better design considering I will be powering multiple 5V modules in the end.