Like many people this afternoon, I read John Gruber’s post — iPhone apps on the iPad — at Daring Fireball with great interest. While I agree with almost everything he said, I disagree with one small point — when the iPad and iPhone OS will become unified. The most current version of the iPhone OS is 3.1.3, but as we all know, the iPad will be released with version 3.2. Many of the changes in the iPad OS are specific changes for that device and were necessary for development.

It’s safe to assume that a new iPhone will be available in June and will probably include redesigned hardware. More importantly, I fully expect to see OS 4.0 on the iPhone at that time.

iPhone OS 4.0 will include lots of new features, just like you would expect to see from Apple. However, It doesn’t make sense for Apple to unify the two operating systems for 4.0 with the timeline they are working with.

Rather, I expect Apple to release OS 4.1 in September or October. It will not only address issues with the 4.0 release, but also unify the operating systems.

Gruber is absolutely right about why we won’t see some apps come to the iPad, from Apple and other developers. It’s not a matter of them not working technically, it’s all about design.

Some developers I’ve talked to said they are starting over with brand new iPad apps. This is a good thing for users — developers are excited about the extra space they have to work with and are coming up with some innovative ideas.

There are some iPhone apps I won’t mind using on the iPad, but if I had my choice, I’d rather use an app designed for the iPad.