You'll have to write your own drivers.
Most carriers charge outrageously for GSM, making it a very expensive way to do tracking comms. I had a look at the SIM908 chipset and it doesn't appear to support anything newer than GSM. Nor does it surface a connector for an external GPS antenna, which means you will need an IP66 enclosure because you'll have to roof mount it to get a lock in weak signal conditions.
To improve reliability and mitigate operational costs I recommend a store and forward architecture, for which this shield is not an ideal choice.
So far as I can determine, the SIM908 does not support altitude. If altitude matters to you then you need a shield that supports a uBlox 5, 6 or later such as this http://www.dfrobot.c...81#.Ui1kDdV-8dU.
I haven't personally used that one but I do intend to test one at some point.