The simple idea behind Maxroam is to save money roaming, on calls, SMS and data. The Maxroam SIM comes with its own mobile number, however you can add local landline numbers from around 60 countries so your contacts can reach you on a local number, without calling internationally.
The new feature I really like is the ability to link an existing mobile number (in my case giffgaff) to my Maxroam SIM so my calls and texts display my giffgaff number as the originating number. This means that replies go back to my usual mobile number. Simpler and less confusing for your contacts, plus they know it's you calling.
Another cool product on the Maxroam website is their iPad micro SIM with a data roaming bundle. Stick this in your 3G iPad when you're travelling and it gives you control and predictability over your data roaming costs.