hmmm interesting, so Sprint allows CDMA roaming on cruise ships (eg. Carnival, Royal Caribbean, etc), so I suppose for those you might need a 55xxx/56xxx based PRL IF you plan to take SOME advantage in roaming on a cruise ship?
Also, I have been doing some research in reference to the Samsung Galaxy S3 and how some providers like Verizon (I dont know about Sprint, but must likely too) has unlocked the GSM radio, or enabled the phone's GSM radio to actually work when you travel internationally, is this true for the SPH-L710T (Triband Galaxy S3)? for Sprint? The only hint that I have here is that the phone gets a "world phone" level of PRL (55xxx) while the Sprint Moto G3 and a Sprint HTC Desre 510 both have the non-world phone based PRL of 25xxx. All what I know is that I have never called Sprint to enable the Galaxy S3 unlock for International use, but based on the article I read, I think Sprint might have auto unlocked its GSM radio for international roaming purposes, or that the Galaxy S3 do come with its GSM radio already unlocked for international use by default.
I though that the "PRL" controlled everything related to the phone's roaming capabilities (well partly its true only for CDMA based networks), I didn't know that a phone could connect to a GSM network offshore totally independent to what the PRL within the device itself says where you can geographically have "service".