Even though they are bare bones, they still require some design knowledge to be very successful. The usage of typographic hierarchy and grids can be seen in all of them - some more successful than others.
Being simple is just as hard as creating more 'fancy' objects, I would suggest having a look into swiss design/ new international style where your sure to be inspired and help see just how people use layouts and typography to create simple designs which work.
Service sounds fantastic, can't wait to see more progress on it!
Also suggestion - I think the design could use some work, have you considered making the grey footer abit bit lighter so there is better contrast with your links?
I would also create real text on your page, for example the "free text messaging groups for friends, family, colleagues" could easily be in text rather than a .gif
Being simple is just as hard as creating more 'fancy' objects, I would suggest having a look into swiss design/ new international style where your sure to be inspired and help see just how people use layouts and typography to create simple designs which work.