@kschulz, Congratulations! Very nice project!
I'm about to make a remote control using the cellular shield and - if that's OK - will use parts of your code and give you the credit.
I'd like to ask you a question: are you using a 5V arduino? (I guess so)
The support guy at sparkfun told me that this shield wasn't intended to be used with 5V I/O (and in fact the datasheet states so...)
I'm asking that because one of my cellular shields (I have two) stops responding sometimes and doesn't accept any command untill power cycled
Thanks
MJ