Though I can identify some technologies like following, I would like to know which ones will surely fail and which ones are worth to test on my old Palm, Symbian, WindowsCE,...
Web
Issues with protocols (HTTPS will be a no go for sure)
Issues with web technologies (css, modern javascript and web2.0 will be a problem too)
Compatible webpages (services with a view or that are still on HTTP, HTML1)
Other technologies
RSS
IM (jabber,....
gopher
...
email
Issues with protocols
Compatible services (POP3/SMTP)
...