I am utterly convinced that people are going to mess up EVERY name out there, at one time or another.

Seriously, my DH has a story about someone mispronouncing the name BOB!
In my experience, most people can pronounce Iain. Some get it wrong, but they probably wouldn't know how to say it without the additional "i," either. I have a Gabriel, and he gets called Gabrielle regularly.

And I thought it was great marrying a man with a very well-known last name (as in, every one who's been as far as middle school has heard of it), and it still gets mispronounced ALL the time. You just can't win!

The great thing with Iain James is that if he does find his first name to be annoying (and I doubt he would), he can always use James, a classic name that is much
less likely to be messed up.