unable to install usbserial driver for GPRS shield with mac air vs. 10.9
The USB serial connection is provided by the Arduino, not the shield, and the naming pattern for an Uno on OSX will not be tty.usbserial### but rather something else (tty.usbmodem### perhaps?).

If I recall correctly, an Uno does not require a driver on OSX though older/unofficial FTDI based boards (as well as unofficial boards based on yet other fixed function chips) do require drivers.

(On Linux it is typically /dev/ttyUSB# for fixed function and /dev/ttyACM# for an Uno, both using kernel module drivers shipped with most distributions.  On Windows they are all COM# and drivers are typically required)