The Google+ Android app works fine.

Screenshot Tour of Google+ for Android

But, the lack of a Google+ iOS app doesn’t mean that you can’t work with Google+ on an iPhone or iPad. Assuming you have a Google+ account, just point the Safari mobile browser at:

plus.google.com

This is the same URL you would use on a desktop. Google will figure out what you are using an redirect you to the mobile web friendly Google+ site. The first screenshot on the left is Google+ rendered in Safari mobile on an iPhone 4.

The second screenshot is Google+ rendered on an iPad 2. You may note that Google+ is not optimized for the iPad’s larger display. It is still usable, however.

FYI: The Google+ mobile web site does NOT work in a Windows Phone 7 device’s browser.