Yes, you can call Puerto Rico without any additional charge. It will only deduct minutes from your airtime if you call during the day from 6:00am to 9:01pm. During Nights: 9:01pm-5:59am and Weekends it's totally free.
I would like to add to this question... I have the Nationwide Premium plan and will be traveling a good bit to Puerto Rico. The coverage map shows most of PR is included in the coverage plan. It also says on the website that "most" areas are included in the coverage of the Nationwide plan and to use the banner as an indicator for what is "roaming". However when you call CS they say it will be a charge of $0.69/min and when you look up the international calling it shows the same. It is contradictory... can anyone shed some light on this?
"Most of Puerto Rico is included in the Nationwide and America’s Choice Coverage Areas. If you roam out of the Nationwide or America’s Choice coverage area, you will be charged $.69 per minute. Please use your device's banner as an indicator of your roaming status. "
That's taken from the International Services page. So from that you can deduct that "most of Puerto Rico is included in the Nationwide" family of calling plans. So there's no additional charge for those area's where you have "extended network" displayed on the phone. However, some areas will have it change to "Roaming" and that's when you're getting billed the .69/min per minute.
As to the specific areas in PR covered by the plan? You can use the coverage map to look up the specific city or zip code where you're going to and see if it's included or not.