Everything wasn’t rosy recently for the Square mobile payment system. It was discovered that the current version interfered with the iPhone’s antenna due to contact with its own metal fitting. Square has just released an updated version of the product that is now compatible with the iPhone 4, thanks to the use of a plastic fitting instead of metal. The device is already shipping and Square will ship the reader to customers for free who have used the app recently. In case you missed the earlier reports, the Square mobile payment system uses an iPhone’s or iPod touch’s 3.5mm audio jack to connect and talk to an app that is capable of reading a credit card and processing the payment through an online system, making it useful for small businesses.