I bought a $10 PIN on CallingMart for both PagePlus and Airvoice ($20 combined, to meet minimum purchase). I applied the current 5% off code for PagePlus, and both PINs received the discount. I don't know if CallingMart usually does have discounts for AirVoice, but I have never received an email notification about it (I do, for the others).
That code is not only for PagePlus but also for Airvoice and others, that's why.
From their FB page:
5% Off T-Mobile, Pageplus, Simple Mobile, H2O, Cricket, Red Pocket and Airvoice refills on CallingMart.com NOW through 09/03/12. Coupon Code: B2S125
Current:Former:Hi, my name is Jairzinho and I've been Wireless Contract-free for 12 years!