[asterisk-users] Different From and contact header

[C F]

I have a provider that in order to set outbound CID they want me to
make sure that the From Header in the sip invite matches the caller ID
while the contact header matches the registration info.
For example.
My phone number with my provider is 2125551212 which is also my
username. I want caller ID to show up as 7185551212. The provider
wants that the header should be like this:

=====begin SIP Headers=====
Adding codec 0x4 (ulaw) to SDP
Adding non-codec 0x1 (telephone-event) to SDP
Reliably Transmitting (no NAT) to y.y.y.y:5060:
INVITE sip:13475551212 at sipxx.sipprovider.com SIP/2.0
Via: SIP/2.0/UDP x.x.x.x:5060;branch=z9hG4bK7d87735f;rport
From: "7185551212" <sip:7185551212 at sipxx.sipprovider.com>;tag=as56382d68
To: <sip:13475551212 at sipxx.sipprovider.com>
Contact: <sip:2125551212 at x.x.x.x>
Call-ID: 21292bde7c00298c2d74c9033bb02c3c at sipxx.sipprovider.com
CSeq: 103 INVITE
User-Agent: Asterisk PBX
Max-Forwards: 70
Remote-Party-ID: "7185551212"
<sip:7185551212 at sipxx.sipprovider.com>;privacy=off;screen=yes
Authorization: Digest username="2125551212",
realm="sip10.xchangetele.com", algorithm=MD5,
uri="sip:13475551212 at sipxx.sipprovider.com", nonce="a718c5ddb60d",
response="7beb31c547f1252dcb9bf10b593b64a5", opaque="", qop=auth,
cnonce="514eefb9", nc=00000001
Date: Tue, 11 Aug 2009 23:51:06 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
P-Asserted-Identity: <sip:7185551212 at sipxx.sipprovider.com>
Content-Type: application/sdp
Content-Length: 220
====End Sip Headers=====

Is that possible? If yes how?


TIA