Adafruit Feather 32u4 FONA
Feather is the new development board from Adafruit, and like its namesake it is thin, light, and lets you fly.
At the Feather 32u4's heart is at ATmega32u4 clocked at 8 MHz and at 3.3V logic, This chip has 32K of flash and 2K of RAM, with built in USB so not only does it have a USB-to-Serial program & debug capability built in with no need for an FTDI-like chip, it can also act like a mouse, keyboard, USB MIDI device, etc.
It also Includes a connector for any of our 3.7V Lithium polymer batteries and built in battery charging.
A 500mAh+ Lipoly battery is required for use, it keeps the cellular module happy during the high current spikes. Plug the Feather into microUSB to charge at 500mA.
Here's some handy specs! Like all Feather 32u4's you get:
Measures 2.4" x 0.9" x 0.28" (61mm x 23mm x 7mm) without headers soldered in
Light as a (large?) feather - 8.2 grams
ATmega32u4 @ 8MHz with 3.3V logic/power
3.3V regulator with 500mA peak current output
USB native support, comes with USB bootloader and serial port debugging
You also get tons of pins - 20 GPIO pins
Hardware Serial, hardware I2C, hardware SPI support
8 x PWM pins
10 x analog inputs
Built in 500mA lipoly charger with charging status indicator LED
Pin #13 red LED for general purpose blinking
Power/enable pin for the 3.3V regulator
4 mounting holes
Quad-band 850/900/1800/1900MHz - connect onto any global GSM network with any 2G SIM (in the USA, T-Mobile is suggested)
Make and receive voice calls using an external 8Ω speaker + electret microphone
Send and receive SMS messages
Send and receive GPRS data (TCP/IP, HTTP, etc.)
Scan and receive FM radio broadcasts (yeah, we don't exactly know why this was included but it works really well)
AT command interface with "auto baud" detection
Pair-able Bluetooth client interface with SPP (for controlling the module) as well as audio.
You will also need some required accessories to make Feather FONA work. These are not included!
Lipoly Battery - 500mAh or larger!
External Mic & Speaker - If you want to make phone calls, you'll also need this electret mic and mini 8 ohm speaker