If you're unsure at all about the PMI, call your servicer and ask about a recast of the loan. In some cases you can put a big chunk (how big will depend on the servicer and your loan) of money and reamortize the mortgage over a new 30 year period. You may be able to get rid of the PMI this way.
A refi is a possibility too if you can match your current rate or come close without paying a ton in closing costs but that's a long shot IMO.
If the PMI stays for 3 years no matter what then:
-Make *sure* it will go away in 3 years (ie you'll be at 80/20 and satisfy whatever other requirements are in place).
-Put all your extra $ in index funds (pay NO extra mortgage payments at all). Expected return there is going to be >4%. This is assuming you don't think you'll need the money in the short term, of course. If you do, stay away from stocks.
There is an emotional aspect too, here - paying off the mortgage is a 100% "safe" investment, so you could choose that as well and not be wrong to do so, depending on how you feel about risk and investment optimization.
-W