I would suggest you to use the LInksys WRT54GP2-NA or the D-link DVG-1120.
THe configuration for the DVG-1120 is as follows:
Asterisk mgcp.conf settings (1120M)
[000abcdef12] ; device's mac address
host = dynamic
context = from inside
canreinvite = no
mailbox=14165551213@default
nat=yes
threewaycalling = yes
transfer = no
callwaiting = yes
callerid="Line 2" <14165551213>
line => aaln/2
context = from-inside
mailbox=14165551212@default
threewaycalling = yes
transfer = no
callwaiting = yes
nat=yes
callerid="Line 1" <14165551212>
line => aaln/1
line => *
Asterisk sip.conf Settings
[1020]
username=1020
type=friend
secret=SECRET
qualify=no
port=5061
nat=never
host=dynamic
dtmfmode=inband
context=internal
canreinvite=no
callerid="1020"<1020>
Note: The CID name inside quotes on "caller id" must correspond to the "display name" field on the VoIP router's page below.
Hope this helps