There is no doubt iOS developers are breathing a little easier today after Apple’s letter to patent holding company Lodsys.

[ad#Google Adsense 300×250 in story]”It’s been the longest ten days that I can remember,” PCalc developer James Thomson, told The Loop. “When I got the original FedEx parcel, I honestly thought somebody had sent me a present. To say I was surprised by the contents would be an understatement.”

Ken Landau, CEO of MobileAge agrees. “There is certainly a feeling of relief, he said.

Thomson was one of the first developers to receive a letter from Lodsys threatening to sue him for using Apple’s in-app purchasing system.

Lodsys maintained that Apple licensed its technology for use in its apps, but was not allowed to allow its developers to use it. Apple clearly didn’t agree.

In a letter to Lodsys on Monday, Apple made it’s point very clear.

“Apple is undisputedly licensed to these patents and the App Makers are protected by that license,” wrote Bruce Sewell, Apple Senior Vice President and General Counsel.

The in-app purchasing system allows customers to try out a lite version of an app, and if they like it, purchase the full app. This can all be done inside the app itself, so it’s very convenient for customers.

Landau said there are a lot of customers that purchase one of his company’s apps, Shanghai Mahjong, using the in-app method.

Apple has been criticized for not speaking up on behalf of its developers sooner, but Thomson said he had faith the company would be there in the end.

“Yes, I always did [think Apple would help developers],” said Thomson. “You can never be sure what Apple will do in any given situation, but our interests were aligned with their interests and that gave me hope.”

It seems clear now that Apple is taking up the Lodsys patent fight as their own. Developers can go back to making apps and let Apple deal with the legal issues — that’s the way it should be.

“Apple has made it very clear that they have our backs, and for that I’m extremely grateful!,” said Thomson. “Now, I am going to have a lie down and a beer, not in that order.”