I suggest you drop the phone interview requirement and conduct your research online; a secure, well-tracked form will do. If it's good enough for Nielsen and Price WaterHouse Coopers, it should be good enough for you.
P.S. Professionals might not be too thrilled about the $25 reward as well.
[Edit: Also try not to pester web-savvy communities too much, or someone might decide to feed your link to 4chan and you will get all the high-quality TIME Magazine-esque data your heart desires.]
I do try to avoid pestering communities, truly I do. Mostly I'm an ordinary participant!
The people you want to interview charge around $100/hour (or more). You're asking to buy >$50 worth of time for a $25 gift card.
Change the offer to $50 payable via Paypal, commit to it taking 30 minutes or less, and you'll probably get some responses.
I did say I was charming... or maybe I just have interesting questions to ask.