Phone settings a barrier to mobile marketing?

According to a post over at Mobhappy, some European companies launching mobile marketing campaigns with SMS opt-ins followed by WAP Push messages are seeing non-response rates of 75 percent--and that's after the user expresses interest through SMS! While a 25 percent yield is impressive for many marketing channels, this channel should be closer to a majority since the user voluntarily signed up. Mobhappy thinks phone settings may be part of the problem, but finds the 75 percent non-response rate much too high for phone settings issues alone. Any thoughts on this? Is this surprising?

For more on Mobhappy's mobile marketing rant:
- check out this blog entry