At present time you have a setup something like is depicted here:
http://www.vonage.com/help_knowledge...php?article=88. What
you need is what is depicted here:
http://www.vonage.com/help_knowledge...php?article=61.
You are allowing both your 4 port and your RT31P2 to handle DHCP which
is why you have two different IP sets. Install your RT31P2 as the
first device after your modem, allow it to handle DHCP. Then connect
your 4 port to the RT31P2 making sure to disable DHCP in it (the 4
port), as you basically only want to use it as a switch and nothing
more. Then connect your computers, in any combination you like, i.e.
all to the 4 port, 2 to the RT31P2 and two to the 4 port, etc.
The other reason for connecting this way, (with the RT31P2 before your
other switch and computers is that it will allow it to handle the
bandwidth management which is recommended for the best quality on your
phone.
Hope this helps.