Changing phone over to Green.com is it worth it?

Have any of you heard of this new phone company 'Green.com' they are advertising on a lot of charitys pamphlets, saying that if you change over to them, you will make substantial savings, and also a certain amount goes to charity.
Am thinking of changing over, does anyone have any experience of them though?
Thank you

Assuming is not the same crowd their name is a bit confusing. Why not just choose the cheapest telecom provider for your particular call usage profile and donate some or all of any savings that you make to charity yourself?