@doragasu It is perfectly useable as a phone, no problems at all. I have a xperia 10 II that is currently in use by a daughter (with the webbrowser hidden) and she does fine. When I used it I did everything including banking without trouble.
It misses the killer feature of the #n900, which was seamless integration of all instant messaging. It supports jabber, but no other protocols out of the box. Granted, n900 existed in a time when facebook and google were xmpp.