I have a lot of experience in SMS but not as much in other payment solutions.
I must say that our customers are very happy with our SMS solutions though. The one that seems to be the best for users is the subscription method. Say a page want a user to subscribe to it's content, then we can in e.g. United Kingdom bill the user between 1.5£-15£ a day. And say a site gets 100 subscribers, that's 300£ if you charge say 3£ (quite typical amount) => 9000£ per month. Then of course there's the operators shares and stuff, but still there's very much money left for the site-manager in the end!
The thing with SMS is that many users believe paying with CC# etc feels insecure and that SMS is as simple as 1-2-3 and also they will be anonymous (what he paid for isn't specified on his invoice)
We have even gone so far that we have a site nowadays with SMS as the only payment option:
http://www.smsvid.com
But in fact the site runs VERY well and we cash in a lot of $$$ with it (available in 9 countries today).
So my conclusion is:
* For bigger payments (100s of dollars range) SMS is not an option.
* For smaller one-time fees (like on smsvid.com) SMS is awesome.
* For subscriptions costing in range between a few pounds/dollars/euros up to around 10 £/$/? SMS is also perfect as the user doesn't have to do more than send in one tiny sms. (For webmasters this can means a lot of $$$ since they can build of thousands of members that continue to use the service and their member db will just grow and grow. I base this on my experience that a lot of users really stay with their subscriptions for at least some weeks but up to months and some forever)
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If you have more questions or is interested in one of these solutions or another you have been thinking of, don't hesitate to drop me a mail!