Tomorrow, those companies will gain a significant competitor when VeriFone launches SAIL, a mobile payment-processing platform for small and medium-size businesses.

Similar to the programs that and PhoneSwipe offer, merchants who sign up with VeriFone's SAIL program will get a free credit card reader that they can plug into their Apple or Android smartphone or tablet, and a free app for processing credit card transactions. The merchant will pay a 2.7 percent fee for each swiped transaction, which is comparable to the other services (Square charges 2.75 percent; PhoneSwipe, 2.69 percent); but VeriFone will also provide its customers the option of paying a $9.95-per-month subscription fee in exchange for a discounted transaction fee of 1.95 percent.

Existing VeriFone customers can also integrate SAIL into their current operations, tying the mobile app to their countertop equipment so they can also accept tap-and-pay cards and near-field communication (NFC) services such as Google Wallet. These features could render SAIL more attractive to larger businesses with storefront operations and/or higher volumes of transactions.

But the feature most likely to set VeriFone's SAIL service apart from the competition is its software development kit (SDK), which can tie its payment-processing service into third-party marketing, customer-relationship management (), and customer , as well as social media tools such as , Twitter, and Yelp. With the customer's permission, the merchant will be able to send a customized, interactive receipt to the customer's email address, too (Square and PhoneSwipe also support email receipts).

The emailed receipt, besides providing the customer with a convenient proof of payment, could also include a note and a link encouraging the customer to post a review of the business on Yelp, or to "like" the merchant's Facebook fan page. This puts the merchant's name in front of the customer's social contacts, potentially generating new business.