State laws seem to be more geared towards Concealed Carry rather than Open Carry. They talk more about where you can/can't CC but don't say much about OC. It is legal to OC pretty much anywhere in the state except places like Schools and Gov't Buildings. You can CC outside the city limits without the necessity of a permit. You can, with a permit, carry concealed everywhere except the above-mentioned locations and Banks, Bars and places where sold, dispensed and consumed in the same room. Legislation has changed the necessity of a permit to CC in the state starting 01 July, 2011.
Next time you have some free time google Montana Codes Annotated and then do a search for Concealed Carry. It will pull up all the statutes pertaining to concealed carry within the state. You sometimes have to read either the fine print or read in between the lines. The statutes say you can't do this so you have to assume that if you can't do this, you probably can do that. It won't always come out and say it, but if you have any questions contact a gentleman by the name of C. Mark Fowler at the Attorney General's office. He's a huge help when it comes to anything pertaining to concealed carry laws.