I don't think you need prior work or volunteer experience to get an internship, but it sure does help.
As a hiring manager, the goal of having an intern on my team is the following:
* I want to find a student who shows promise for future work at my company.
* The internship is a way for me to gauge the talent of the student and see how they do during the summer.
* Supporting an intern will take resources away from my team (helping them get up to speed, checkins, etc), but it's worth it if my company benefits from getting a bright future employee.
Given the goals stated above, I definitely love seeing volunteer or prior work experience (even if it's irrelevant to the field I'm hiring for). The reason why is that it shows that the candidate has had experience working in a non-school environment, and thus is more mature. More maturity means less things that can go wrong, as expectations are better set, and less work for the team to bring them on-board.
If you happen to have the time, I would encourage you to go volunteer with the skills you already have and give back to the community that helped make you who you are today. I personally like giving back through catchafire.org, and would encourage others to do the same.
I wish you the best of luck in your future!