I would have thought that Sparkfun designed the board with its high current regulator to be able to drive the GSM unit from the 5v supply.
Regardless running from a 12v 2.5A psu there is No voltage drop or fluctuation from the 3.3v, 5v, or Vin +12v lines when sending a SMS.
And Like I said, it ALWAYS sends one SMS and it is DELIVERED to my phone.
Code dont fit in one post
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