Hmm.. there is something undocumented that you could try out.. if you look at the latest schema (for the 7.0 ip phone services developer guide) you there's an element called KeyItem which you can have for pretty much any CiscoIpPhone object (basically those that also can have SoftKeys).. the type is CiscoIPPhoneKeyType, you can have 0 - 32 such items, and there's an attribute that seems to indicate where the keys go.. keypadTarget can go to application (default), applicationCall or activeCall.. perhaps one of the latter two allows keys pressed to go to the telephony context and not the app context.
CiscoIPPhoneKeyType has a key (can be any of the physical keys.. you'll find a listing of what the values are in the schema file), then an url, and an urldown url.
So, either you manage to simply define those keys with some url (perhaps it can be empty? to be tested..) and manage to have them routed to the telephony context with the attribute I mentioned, or you could simply define a KeyItem for each key you want to be active, define an url for each and make this a notify url.. that way your app gets a notification about the key pressed, and you can do with it what you want.. this requires some additional logic on your end as you need to gather digits and decide when to initiate the call, but it still sounds doable.
If you go down that route, please let us know your findings because as I said, those things are only in the schema and there's no documentation that outlines the use - thus it would be useful for the rest of us if you could tell us your findings.
