asterisk users - Jan 2004 - Net2Phone error 407: Unauthorized

I'm trying to register with net2phone. I've already 
changed chan_sip.c, User-Agent: string to say "User-Agent: 
Cisco ATA 186 v2.16 ata18x (030401a)". But still I'm 
getting the error msg. Here is the debug msg:

IP Address is xxx.xxx.xxx.xxx
11 headers, 0 lines
Reliably Transmitting:
REGISTER sip:66.33.146.12 SIP/2.0
Via: SIP/2.0/UDP 
xxx.xxx.xxx.xxx:5060;branch=z9hG4bK0b4de3e9
From: <sip:xxxxxxxxxx@66.33.146.12>;tag=as3b2ba80f
To: <sip:xxxxxxxxxx@66.33.146.12>;tag=as3b2ba80f
Call-ID: 0af541053ffa19a36e9dfa4a585934bf@192.168.1.1
CSeq: 102 REGISTER
User-Agent: Cisco ATA 186 v2.16 ata18x (030401a)
Expires: 120
Contact: <sip:xxxxxxxxxx@xxx.xxx.xxx.xxx>
Event: registration
Content-length: 0

  (no NAT) to 66.33.146.12:5060
Sip read:
SIP/2.0 407 Unauthorized
Via: SIP/2.0/UDP 
xxx.xxx.xxx.xxx:5060;branch=z9hG4bK0b4de3e9
From: <sip:xxxxxxxxxx@66.33.146.12>;tag=as3b2ba80f
To: <sip:xxxxxxxxxx@66.33.146.12>;tag=as3b2ba80f
Call-ID: 0af541053ffa19a36e9dfa4a585934bf@192.168.1.1
CSeq: 102 REGISTER
Contact: "net2phone" <sip:66.33.146.12:5060>
User-Agent: Cisco ATA 186 v2.16 ata18x (030401a)
Proxy-Authenticate: Digest 
realm="net2phone",nonce="8A217912713C11886D18CCCC9D300F5B"
Content-Length: 0


10 headers, 0 lines



Here is my sip.conf file:
[general]
port = 5060
bindaddr = 0.0.0.0
context=from-sip
register => 7147036xxx:xxxx@66.33.146.12/7147036xxx
canreinvite=yes
[66.33.146.12]
type=friend
secret=xxxx
username=7147036xxx
host=66.33.146.12

Here is the extensios.conf of sip portion:

[from-sip]
exten => 7147036xxx,1,Dial(SIP/7147036xxx)

Please give an idea how to solve this. If you get success, 
send me the conf files.

Thanks in advance,

Solaiman.