A easy to use and stable user interface in applications for learning is essential! Using SMS on the mobile phone side of the application is one alternative. Using "social software" systems like Blogs, Facebook and Twitter together with SMS could be an intresting alternative.
I tried Twitter together with Blogger, you can se the results on my "Reseblogg" (http://bnyres.blogspot.com): I send a SMS to Twitter and my SMS then shows up in the blog!
I also installed Blogger Go on my mobile; it makes it very easy to send MMS to the same blog.
There are many applications linking SMS to a web interface. Linking SMS to Learning Management Systems like Moodle may also be an attractive alternative