Cisco 7911g don't receive incoming calls from elastix 1.6

I’m a newbie testing with voip infraestructure, and i have the following problem:
I have configured an elastix 1.6 as pbx with 4 extensions:
2 extensions as softphone with zoiper. both extensions are working fine.
2 extensions with 2 Cisco IP phone 7911g with the firmware version sip. 8-3-1

I can make calls between both softphones without problems.

60267 11.850904000 SIP/SDP 910 Request: INVITE sip:313@;rinstance=6ca04e9cdffa4235;transport=UDP | 5060 274

But with the 7911g, is only possible to made call to the softphones extensions. I can’t to receive any call in the 7911g.

5060 1245.966778000 SIP/SDP 808 Request: INVITE sip: | 5060 41202

I have copied two captures form wireshark and i think that the problem is in the Request: INVITE:
With the softphone appear the extension and ring correctly, but with the hardphone doesn’t.

Any suggestion?

Thanks a lot

I have been doing some test, and i have detected the followin:

With this command
asterisk -rx “originate SIP/315 application Playback hello-world”
the extension doesn’t ring

But with this command

asterisk -rx “originate SIP/315@XXX.XXX.XXX.XXX application Playback hello-world”
where XXX.XXX.XXX.XXX is the ip of the cisco phone, the cisco ring.

What config should i modify in order to make the extension works correctly?