If you have a Square card reader from squareup.com and an iPhone 4 then you have probably been a bit frustrated with it not working out to well. The problem is the metal to metal contact of the Square reader and the iPhone 4 metal antenna. Yes the antenna curse effects more then just your precious calls.
I ran into this issue in a real life instance of using my Square reader. I was trying to take a deposit from a wedding client today while sitting in Starbucks. I am pretty sure the whole store stood and watched as I swiped the card at least 30 times before deciding to slightly pull up on the attachment and try that. In the past with headphones on other devices I have had connections wear out and then work when I did this, so it was just a logical thing to try in my opinion. It worked! I was able to take my payment. Square is a much better option for me then Google Checkout or Paypal because of the lower rate Square offers when the card is swiped.
When I got home I decided to go online to see if anyone else had this issue, I found this post confirming my suspicions. I, like the commenter BikeHugger, did not like the suggested paper fix. I did not want to carry around a piece of paper or have to perform that fix in front of a client about to hand me their credit card for a large purchase. Knowing for sure that it was the metal to metal contact I went around my house looking for some sort of epoxy or clear resin I could apply to the base of the post on the Square card reader attachment. What you see in the video is what I came up with.
In this video I explain the process of applying a fix to this issue.
*Finger Nail Polish Top Coat or Clear Epoxy (see below)
*Q-Tip (Not the rapper from A Tribe Called Quest silly)
Hope this helps you with your credit card processing-ness.
Update: After inserting the Square card reader into the iPhone 4 about 10 times the finger nail polish top coat wore off. I decided to take a trip to Orchard Supply to get something a little more durable. Elmers Epoxy is what I ended up using.