Reportedly most (All?) operational cellular carriers on Puerto Rico have activated "universal roaming" service. All working towers will accept roaming connections from any phone from any carrier (or no service provider). You may need to turn the phone off & on so it scans for a working signal.
Roaming still requires a working cell tower. 48 counties and county-equivalents in Puerto Rico have 0% cell sites working. Less than 25% of cell sites in the remaining counties are working. Capacity is extremely limited, so use SMS/Text rather than voice or data.
A side-effect of universal roaming is lack of billing, so expect carriers to announce they are waiving charges and overages in Puerto Rico.
