[noob]

So you have a external DSL modem connected via USB.

I assume its only a single port, and cannot be connected except via USB.

There are 1 of 2 things you could do.

1. If the voyager modem connects to the phone via RJ45

Use a wireless router/modem to connect directly to the phone line.
Connect the voyager to the wireless via the internet port.
Put the logon creds onto the wireless, and remove them from the voyager (tell it it doesn't need to logon for internet).

or

2. If it uses RJ11/BT/etc (other phone plug), and the wireless has RJ45 internet connections
Connect the wireless to the RJ45 LAN socket of the computer
Bridge the connection to allow direct passthrough
Tell the wireless it doesn't need password/etc to connect to the internet.

If it doesn't have a RJ45 modem port just connect it to the computer via a standard RJ45 port, on one of the standar outlets.

Make sure you use WPA security and MAC filtering on the wireless.

If you need it I can make a quick mockup in paint and post it.