The GPRS Shield provides a way to communicate using the GSM cell phone network. The shield allows you to achieve SMS, MMS, GPRS and Audio via UART by sending AT commands. You do need a Sim with data activated. I went with a GiffGaff sim (this is an affiliate link) and put a data package on it, but you can go to an unlimited SMS package for around £7.50 a month if you will be using the shield / sending data regularly. (correct at the time of posting)
This is a nice project that came up on Kickstarter and I supported – I can’t wait to get this shield (1Sheeld). The idea is that it gives you easy access to all the capabilities on your Android device, all through the one shield, so you now wouldn’t have to connect loads of separate shields or sensors to have control.
At a glance it seems to be a great way to make easier connections, especially if you want to test something out and not pay for a shield / sensor etc to try something.
I haven’t tried it yet but anticipate to have it here around May 2014, so hope to post an update with information then. You can purchase these from their site now too.