If you are sending out instructions in advance of the event, you can let those know who may come with an unsupported phone (Blackberry, Windows Phone, Flip Phone) or without a phone, that you will have bidding stations available.
In most of our messaging, we tend to say something like this:
NO SMARTPHONE? NO PROBLEM!
If you do not have an iPhone or Android phone, you can still bid in this auction! We will have iPad bidding stations available at the event and volunteers ready to help you place a bid. Once you arrive, be sure to check-in and get a bid number so that you can use on the iPads.