Easier than you may Think
In addition to the name of the controlling agency and the frequency, sectional charts also provide information as to when Restricted Areas may be in use. When you see the time of use printed on the chart as "continuous" that doesn't mean the airspace will be in use continuously during the times indicated. What it really means is that it COULD be in use during those hours. Odds are that it will NOT be in use when you call. Flying an extra half-hour out of your way in order to avoid a 15-second radio call is really wasteful. When I'm instructing, I have my student plan a dual cross- country flight that on a direct route would take them through a Restricted Area. While in flight I have them call the controlling agency to find out if the airspace is in use. Sometimes it is; sometimes not. In either case the student has learned how easy it is to call and find out. Center is not just for heavy iron.
For whatever reason, probably because they weren't properly trained either, many flight instructors convey to their primary students that calling to see if a Restricted Area is "hot" is a waste of time. You are going to get told to stay out. Since in the real world the opposite is true, those same instructors need to rethink how they teach this particular bit of information. With the advent of $4.00+ AvGas and concurrently rising rental rates, flying through Restricted Areas that are not in use is becoming an increasingly attractive alternative. Call and ask.