1st - buy a 2nd N900 as backup, this should cover 4 to 5 year of usage, by the end of that time 3G/edge and wifi on G would really be too slow and may no longer be available on public networks

2nd - some android phone

3rd - ixxxx

4th - dump phone + n900

5th - dump phone + some android "tab"

the last - when the hell freezes over - WP7