Problems building for iOS, and unsure if upgrading to Unity 4 will fix it?

I have a free version of Unity 3.5 and also have the iOS 3 and Android 3 add ons from when they were given away free for a limited time in April 2012.
I hadn’t used Unity for a while due to other projects, and have now tried to compile a project using Vuforia only to find that there are build errors due to the fact that I am using Xcode 4.5 / iOS6 (at least that’s what this post suggests xcode build fail - Mach-o linker error - Questions & Answers - Unity Discussions).

What I am unsure of is, if I update my free Unity to Unity 4, will I still be able to use my iOS add on?
At the moment this project is speculative, so unfortunately we are not in a position to pay for the Pro version until we get funding. We are in the awkward position of needing to be able to build prototypes first, so we can show clients prior to them agreeing to fund the project. However without the iOS add on working we cannot build a working prototype.

Does anyone know if upgrading Unity will fix the problem?

Thanks

If you upgrade from 3.x to 4.x, you’ll need to pay to upgrade the iOS and Android add-ons. Just enter your serial number into the webstore, and you’ll get shown the upgrade price. Don’t forget to tell the store you want to upgrade the add-ons.