I've got a call twice from this number.  No voicemail left.  I don't have a 406 area code, but do live in Montana, so it's probably not a wrong number.  Called at 9:30 pm on 24 April and 8:35 on the 22nd.

My guess it's something political or something.

I say in my out-going voicemail message, if you want me to return your call, you best leave a voicemail.  Nowadays if I get a call, if it's not from one of my contacts or a number I recognize, I don't answer.  If it's important, they can leave a message.