My experience with in-flight message-only WiFi is that they're just really slow and the ping times are long. Some services are actively blocked, e.g. Skype wouldn't work at all even for text messages, but browsing the internet is usually allowed. My VPN wouldn't work, but I suspect it might have if I used an obfuscated connection instead of OpenVPN or whatever the default is (e.g. over SSL). I could load GMail in the browser and Wikipedia probably would have worked. It's strongly website dependent. Hacker News is extraordinarily resilient to lousy connections and generally the index would always load without any trouble. It works even on a 3 second ping over satellite internet. Very few websites are that tolerant.
The flight crew (BA) knew what's up. They specifically warned us to check which package we were getting, because evidently they get a lot of complaints when people buy the message-only bundle and are surprised that nothing works.
Singapore gave out free passes for single devices last time I flew with them. It was possible to rotate MAC addresses by forgetting the connection and then re-joining. The connection was quite good, you could watch YouTube in potato resolution. It's quite fun to chat to people and send them photos out of the window.