The phone interview was slated to be an hour long, started on time and was 1 hour exactly. It was the 2nd such interview, and I have a 3rd scheduled. No idea how many more rounds there will be. It began with a brief questioning of my past work experience, and soon moved on to technical questions largely covering data structures and algorithms, from simple (calculate change for a cash register) to complex (knapsack problem, dynamic programming). I was also given a design problem of an e-commerce site and asked to describe some of the basic objects I would need for customers, inventory, orders and shipping, and their interactions. I was expected to provide a pseudo-code solution to the data structures and algorithms questions, which made pen and paper a necessity. It might be more helpful to sit at a computer and actually code up the solution in something like PHP or Python. The interviews have (thus far) been very nice and tolerant of you not reaching a complete solution to the problems on your first iteration. They may even help walk you through a tough part.