3448 will have customer metro ethernet coming in for SIP only, customer also has a cisco asa with their public inet coming in.
I will configure a voice only vlan with the phones getting DHCP from the 3448 - Where should I configure the intervlan routing? I need the phone network to talk to the data network although i only want SIP communications flowing obviously only through the Metro-E on the 3448.
Configure it on the 3448. You'll need to enable IP routing and possibly a route-map or possibly just a static route to the SIP destinations pointing to the Metro-E. Data network will need an IP assigned to a VLAN interface on the 3448 and a static route to the ASA (probably default route).