Question : VoIP over VPN from home to office

My company uses an Asterik VoIP service (SIP protocol), and a VPN gateway on an ISA server.

I telecommute and currently use a softphone on my laptop that puts me on the VoIP network via VPN, so I have an office extension, can make outgoing calls, etc. However, when I dial an extension directly (or have my extension dialed directly), the receiving end does not receive audio from my end (I can work around this by dialing the office number and dialing the extension as if I were calling from outside).

What I would like to do is use a desk phone - not sure if that will resolve the audio problem, but if it does that's just a bonus. I have a Grandstream "IP phone" (not sure what the terminology is, but it connects via ethernet) that everyone else uses in the office. I've been working with the network admin to figure out what configuration we need to make this work, but so far we haven't come up with a solution that we know will work.

I've thought that simply adding a VPN router on my home network will get the phone on the office network, but the SA says the phone will not be able to procure an IP from the DHCP server at the office, as an IP is required to route VPN traffic, and the phone isn't a "smart" device and can't do that.

So the question is, will a VPN router work, and if not, what requirements must be met to make it work or what alternatives do I have?

Answer : VoIP over VPN from home to office

If you could get a hardware router (example: sonciwall firewall), with a vpn to work with the vpn for ISA server.... "site to site"... it could be done.  It could be setup so that you still have an inside ip address.

What they are un-candidly telling you, is that they don't want to spend the money or put in the time to make it work, for a single user's phone....

Can it be done ?...absolutely !... I have users in remote sites all over the place using both hard and softphones.