Miami, Lauderdale, St Thomas, San Juan, Key West, of course the mainland ports I expected native signal and got it. Kept it for quite some time actually after the ship left the port. Friend of mine texted me during dinner to hangout
"Sorry dude, I'm about 10 miles off the coast of FL right now."
St Thomas and San Juan have full Sprint coverage. I was able to do 3G the whole time in port, and chat with my mother as we were leaving the port and going past the forts.
Key West same. In fact I was on the phone quite a bit because the cruise was the first of the month, and silly me forgot to pay the CC bill. Thankfully that was resolved without having to use the ship's internet cafe.
On the Imagination cruise, on a whim I turned off airplane mode just to see what would happen. Got Cellular at Sea on my screen. A few texts came in, and I turned it back off. Never sent a text, and never made a phone call. Once I lose native signal, I just don't care really. A cruise is a vacation, a vacation is an escape. I don't want to be too tethered to the rest of the world thank you very much.
I did use the internet cafe once on my 7n in 2009. On Wednesday. I needed to log onto my work's internal site and look at my schedule for the week I got back so I knew what to expect ... since I was going right back to work the day after the cruise.