usage - Is there any difference between 意外に and 意外と?

I hear　意外に and 意外と used frequently to mean "moreso than I thought." They seem to be interchangeable. Example:

意外と簡単でした = Easier than I thought

Are they both grammatically correct? Is there a difference in nuance or usage using ni vs to? I don't recall ever hearing them used with a present or future tense verb. Can you think of an example where they might be used outside of past tense?

Answer

Take a look at the blog post on http://d.hatena.ne.jp/hiiragi-june/20080528

To summarize:

意外に feels more like written Japanese and 意外と is more colloquial. They both grammatically correct and they both have the same meaning. Although 意外に feels more traditional.

The rest of the blog post is about history of dictionaries and some dictionaries actually don't even talk about the difference between these two.

According to http://dictionary.goo.ne.jp/leaf/jn2/10029/m0u/%E6%84%8F%E5%A4%96/

[補説]現在では「意外に」と同様、「意外と知られていない事実」のように「意外と」の形も用いられる。

Which means

Currently, in the same way as「意外に」, 「意外と」has been used like 「意外と知られていない事実」

So to answer your question, yes they are pretty much interchangeable. Note that に and と are generally not always interchangeable, but in this special case it is.

Also note that the meaning of 「意外に」and 「意外と」has more to do with something not matching one's expectations and expressing one's surprise, so it is more accurate to translate it as "unexpectedly", rather than "more so than I thought", although in some cases it means "more so than I thought". I know I'm being nit-picky here but just want to make sure you understood it right.