I’m looking for an arduino mega cellular shield to substitute the Sparkfun cellular shield - MG2639. Any tips?!
you can use any shields like SIM800 any series, SIM900 and ...
if you want a complete shield that have a GPS/GPRS/GSM and Bluetooth in one module its good
to use SIM808 Module or Shields (i upload a photo from this)
SIM800L is the cheapest option ! (like photo)
this modules uses serial port (Rx/Tx) for running and communicating with your Mega board