I was planning to do a GPS tracker using the Arduino Ethernet, but the main problem is to connect the Arduino to the Internet.Was wondering what kind of modem should I use. Any tips?
Are these kind of GSM modules easy to use do they come with good documentation/samples?
If you are in a region of the world that uses GSM/GPRS cell phones (75-80% of the world uses GSM, in the USA AT&T and T-Mobile use GSM but Sprint and Verizon do not), you might want to use this shield, which would allow you to put in a SIM card: http://www.seeedstudio.com/wiki/GPRS_Shield. You will have to figure out how what cell phone options for the SIM card.
You can also use Wifly + Mifi from any mobile provider.