Feeling comfortable with making a payment from your mobile phone via a tap or a wave? Search for a store based on location before a coupon guides you in. eMarketer estimates this type of payment -- also known as "proximity mobile payments" -- at point of sale in stores in the United States should rise 234% by the end of this year. Total transaction volume should reach $62.24 billion by 2016. The data firm bases the estimates on several assumptions.