The employer first described the position I'd be working on, mostly that I'd be working on server-side microprocessor design. He answered any questions I had on this, and then moved onto questions.
My questions were the following: One based on capacitors and different initial conditions (boundary conditions)
Another based on the diffeq of a RC circuit
At the end we discussed some more about myself and what I'd be interested in.
There was only one phone interview as this was for a co-op, and the interview in general had a relaxed environment. I got the interview from applying through my school's career center in the co-op program, and as for preparation I studied some basic circuitry analyses as most ECE interview questions are based on the EE curriculum