Q. Will I have to pay income taxes in both states?
A. Yes. Or more accurately, you should file returns for both states. OR will give you a credit for what you pay to MT, so there will be little or no double taxation.
Alternate answer: Yes, but "nobody" does. See http://money.cnn.com/2013/06/28/pf/taxes/business-traveler-tax-threat/ If you live in a state without an income tax (e.g. FL or TX), it’s more likely you should file in the work states. You can't use the "it all comes out even" rationale for not filing.
It sounds like you'll be working in MT often enough ( every 6 weeks or so to work in the office for a week) that you should file a MT return, to be on the safe side.
