thanks for all replies...i think i am getting some clues
let me just put more clarity

1. i would like to use only one AOR (sip or sips)... for all kind of
SIP services

2. there is only one instance of sip stack and one generic UA which is
required to route each incoming request to an appropriate application
running over it in the user-device. And only UA does the common
registration using AOR and bindng with dynamically allocated IP
address as contact.

3. There are multiple applications which are using single instance of
UA and sip stack.

for the example sake assume 3 application
A. Push-to-x and VoIP app
B. Messenger with Session-based messaging support using MSRP
C. An interactive game

All 3 apps can expect INVITE request for their corresponding session.
And the remote party who is sending an INVITE can send it for any of
the 3 types of sessions.

Scenario 1.
UA doesn't use a unique user part for each function/application during
registration (as Paul suggested). Hence there is only one contact in
the location server.

So UA will receive INVITE with a Request-URI which is the contact
registered. Now how does UA route this request to appropriate
application?

My Guess - it is not possible unless some std parameter is used for
std service indication in a particular sip header. And this has to be
filled by caller. Same std parameter will be used by applications to
register locally with UA in a device.

Personally i am looking for this solution.

Advantage - This way intelligence is with clients rather than servers.
Solution becomes more flexible.

Scenario 2.
UA may use different user part for each type of application during
registration. But these user parts are not public. Caller still has to
use AOR.

Issue - then how does server on receiving the request selects the
appropriate contact and use that as Request-URI such that on receiving
the request UA can route the request properly to the application?

Can i use RFC 3840 (Indicating User Agent Capabilities in SIP) here in
scenario 2? If yes then what is the role of server and UAC/UAS? I
guess RFC does not clearly define that.

RFC 3841 (Caller Preferences) gives some mechanism to select from
different contacts. But couldn't find exactly how different types of
services can be incorporated. There has to be a field which can filled
with any text and only callee and caller should understand that. And
this field can act as an application or service type parameter.

regards,
-nins

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