My environment is asterisk 1.4, from the console, I see the error is:
"Failed to authenticate on INVITE to xxxxxxx"
I tried software phone and ATA, it works well

Below is from my sip debug output, would you please take a look and point me out?
Thanks
Shawn
--------------------------------------------------------------------------------------------------------------------------------
-- Executing [9059515000@default:1] NoOp("SIP/99-00610df8", "") in new stack
-- Executing [9059515000@default:2] Dial("SIP/99-00610df8", "SIP/19059515000@fpl1|120|tT") in new stack
Audio is at 174.138.206.153 port 10074
Adding codec 0x4 (ulaw) to SDP
Adding non-codec 0x1 (telephone-event) to SDP
Reliably Transmitting (NAT) to 208.65.240.165:5060:
INVITE sip:19059515000@voip.freephoneline.ca SIP/2.0
Via: SIP/2.0/UDP 174.138.206.153:6631;branch=z9hG4bK26111f17;rport
From: "14164778887" <sip:14164778887@174.138.206.153:6631>;tag=as7a392dfc
To: <sip:19059515000@voip.freephoneline.ca>
Contact: <sip:14164778887@174.138.206.153:6631>
Call-ID: 68af4e2e1dc4c9353a8406d309a8963d@174.138.206.153
CSeq: 102 INVITE
User-Agent: Linksys/RT31P2-3.1.6(LI)
Max-Forwards: 70
Date: Sat, 25 Aug 2012 16:24:37 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Supported: replaces
Content-Type: application/sdp
Content-Length: 244
v=0
o=root 8400 8400 IN IP4 174.138.206.153
s=session
c=IN IP4 174.138.206.153
t=0 0
m=audio 10074 RTP/AVP 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=silenceSupp:off - - - -
a=ptime:20
a=sendrecv
---
-- Called 19059515000@fpl1
OpenWrt*CLI>
<--- SIP read from 208.65.240.165:5060 --->
SIP/2.0 100 Trying
Via: SIP/2.0/UDP 174.138.206.153:6631;branch=z9hG4bK26111f17;rport=6631
To: <sip:19059515000@voip.freephoneline.ca>
From: "14164778887"<sip:14164778887@174.138.206.153:6631>;tag=as7a392dfc
Call-ID: 68af4e2e1dc4c9353a8406d309a8963d@174.138.206.153
CSeq: 102 INVITE
Content-Length: 0
<------------->
--- (7 headers 0 lines) ---
<--- SIP read from 208.65.240.165:5060 --->
SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP 174.138.206.153:6631;branch=z9hG4bK26111f17;rport=6631
Record-Route: <sip:208.65.240.165:5060;transport=udp;lr>
To: <sip:19059515000@voip.freephoneline.ca>
From: "14164778887"<sip:14164778887@174.138.206.153:6631>;tag=as7a392dfc
Call-ID: 68af4e2e1dc4c9353a8406d309a8963d@174.138.206.153
CSeq: 102 INVITE
Server: Sippy
WWW-Authenticate: Digest realm="voip.freephoneline.ca",nonce="13610bd079376096859b4db3c50eb925742b"
Content-Length: 0
<------------->
--- (10 headers 0 lines) ---
Transmitting (NAT) to 208.65.240.165:5060:
ACK sip:19059515000@voip.freephoneline.ca SIP/2.0
Via: SIP/2.0/UDP 174.138.206.153:6631;branch=z9hG4bK26111f17;rport
From: "14164778887" <sip:14164778887@174.138.206.153:6631>;tag=as7a392dfc
To: <sip:19059515000@voip.freephoneline.ca>
Contact: <sip:14164778887@174.138.206.153:6631>
Call-ID: 68af4e2e1dc4c9353a8406d309a8963d@174.138.206.153
CSeq: 102 ACK
User-Agent: Linksys/RT31P2-3.1.6(LI)
Max-Forwards: 70
Content-Length: 0
---
[Aug 25 12:24:37] NOTICE[574]: chan_sip.c:12377 handle_response_invite: Failed to authenticate on INVITE to '"14164778887" <sip:14164778887@174.138.206.153:6631>;tag=as7a392dfc'
-- SIP/fpl1-00614d88 is circuit-busy
== Everyone is busy/congested at this time (1:0/1/0)