Asterisk: Google voice issue

Hi guys,

I have been working on Asterisk 11 with OpenWRT (barrier breaker).

I set up google voice configuration in asterisk config files. It is working fine for both outbound call and inbound call.

However,
If I make outbound calls from asterisk to the remote phone, it works fine and a person can talk properly. But after hanging up that call, my asterisk is ringing itself (getting inbound call automatically – confirmed from the log). (it is happening with each outbound call)

[note: inbound calls work perfectly fine]

my files:

extension.conf:

[general]
static=yes
writeprotect=no
clearglobalvars=no

[globals]

[incoming-local]
include => outgoing-google
include => outgoing-sip

[incoming-analog]
include => outgoing-google
include => outgoing-sip

[incoming-softphone]
include => outgoing-google
include => outgoing-sip

[outgoing-google]
exten => _.,1,Set(CALLERID(name)=12345678900)
exten => _.,2,Dial(Motif/google/${EXTEN}@voice.google.com,20,r)

[incoming-motif]
exten => s,1,NoOp()
same => n,Wait(1)
same => n,Answer()
same => n,SendDTMF(1)
same => n,Dial(dahdi/1,20)

motif.conf
[google]
transport=google-v1
context=incoming-motif
disallow=all
allow=ulaw
connection=google

Any suggestion guys???

Thanks