I am not sure how to do it on the phone app. But when you log onto listia.com from a computer you are able to click on a blue Get It Now button right under where you put in your bid. =]
I switch back n forth between the app on my iphone and the web. Its easier for my to type on a keyboard so I dont know all the ins and outs of the app lol. It was just a guess
Well I signed up for it years ago but I think its pretty much the same. you create a username and password and then you link a bank account or debit/credit card. Once you do that you can pay for items from people who have a linked email or local businesses or ebay =]