Here is the modem library for Arduino: Google Code Archive - Long-term storage for Google Code Project Hosting.
and here is the iOS library: Google Code Archive - Long-term storage for Google Code Project Hosting.
The project was made in 2012 so the code is a little dated (odd that so much changes in two years) and I had to rebuild the project to get it to execute. I plan on writing a cordova plugin to send data back and forth between javascript and the native code so I'll post that once I get it all put together.