The idea would be nice... yet it won't work "over the ocean".
I would have to make an account with a firm over there (and they want some fees, and the money is then *still* in America and not in Germany... I still have the problem how to get it over here).
Also... perhaps you haven't noticed as you live in the US, but with these Dial-Services here have been countless lawsuits from parents whose kids spent hundreds of Euro talking to some hotlines... and this is also what I am afraid of
also if you have "say how many you want to donate and it gets subtracted from your phone bill" ... who guarantees that only the owner of the contract with the phone company donates? what if his friend visits, dials the number and says "want 500 bucks in there"...
I sense much more hassle than benefit
(that's what I like at paypal, you need a credit card for it, the money is here in seconds and I stil can refund without costs if there are problems... and it is safe as nobody except you knows your password).