Update: Jason Fried responds

Shortly after our post went live, 37signals founder Jason Fried left a comment, clarifying that they are toying with the design of the sign-up page, but that all of the old plans are still available.

"While we used to have four plans on the sign up chart, today we only have three," said Fried. "Same prices as before, just fewer plans displayed. A while back we used to have six plans to choose from, but we found that was ultimately confusing customers. So we went to five. Then we went to four. Now we're experimenting with three."

Fried echoed Hansson's earlier statement that the changes are purely experimental and that they may continue to alter the plans listed on their sign-up page, depending on their findings.