Square hit the market with a bang. An innovative small piece of hardware took advantage of the microphone feature of a smartphone’s headphone jack to create a way to read a credit card and interact with software on the smartphone. You can buy a Sqaure at Target for $9.99 and I believe you get a $10 credit from Square. They make their money via a percentage of the transaction but you don’t need a merchant account.
Now Paypal is getting in on the "anyone can accept credit cards" game. Paypal is offering their smartphone card reader for free. Soon, your excuse of "I have no cash" to say no to Girl Scout cookies and Boy Scout popcorn will be gone!