On my Treo 650, is there a way to make "Favorites page 2" reliably
come up as my initial page when I power on the phone?

Not that I know of.  But you can come close by using these two programs:

Treo Shortcuts - $5 Shareware
This gives you an icon that you can launch to go to the Favorites view
of the phone app, but just the first screen, not the second. Maybe you
can ask the author to make the second through tenth screens available
as options.
http://www.palmgear.com/index.cfm?fuseaction=software.showsoftware&PartnerREF=&siteid=1&prodID=55846
or at the author's site http://www.shsh.com/products/index.html

AutoExec 2.00 - Freeware
This allows you to have any program launch automatically upon power-on.
If you ever find a program that lets you jump right to the second
screen of the favorites view, you can use AutoExec to run it at
startup.
http://www.freewarepalm.com/utilities/autoexec.shtml