Some good phone interview questions are:
Are you currently employed? If yes, why are you considering leaving? If not why are they not?
Why'd you leave your last job?
If they have prior work experience ask they what their favorite job was and why. What was their least favorite job and why.
What made you want to apply to our ad? - helps to gleam if your prospecting process is attracting the right people or what you can use in the future to improve it.
How flexibile are you? Are you willing to work some late nights and some weekends?
Many employers focus on their own expectations of the potential employee are but rarely do you see many ask what the employee expects of the employer. It is a pretty vital question in my opinion that helps to create a company culture that allows the individuals to grow as well as the business. Your expectations of the employee are important but if you build a business where employees can easily plateau you're going to have a high turn over rate. Also some people just have unrealistic expectations of what their job is suppose to provide them, it saves you a big headache figuring out those who want a lot for very little effort on their part early on.
For the in person interview, find a basic math test and see how well they do. There are quite a few out there that ask things like find the area of this shape/room, etc. You could make your own for calculations you do daily when it comes to mixing products, pricing, etc.