Transaction fees on credit cards vary widely across industry, and even from contract to contract. But if you're a business owner considering a mobile-swipe service, here is an that lets you compare rates from Square and VeriFone, based on average transaction size and monthly volume.

These services offer inexpensive, compelling to traditional credit-card systems. And while Visa's investment does offer needed validity and backing to the infant industry, business owners who use these services should be wary of too much meddling from the few big players, as it will undoubtedly prevent any real reduction of fees by the disruptive technologies entering a highly controlled industry. Square must proceed cautiously with its new backing, because such fees have kept many small business owners from jumping on the credit card bandwagon in the first place.

Ilie Mitaru is a culture and business journalist and occasional entrepreneur. He is the founder of an alternative business magazine, Stake, set to launch in June.