Registering a SIP phone but seeing warnings

When I use an application on a cell phone to register itself with asterisk I get the following warning:

[Dec 30 11:18:00] WARNING[16730]: chan_sip.c:12951 handle_response: Remote host can’t match request NOTIFY to call ‘45ad2e1f63f563d02aaef28e50ec14ce@’. Giving up.

I do see (using wireshark) that the application registers but then asterisk sends a “REQUEST NOTIFY” to the phone. The phone responds with a “STATUS 481: SUBSCRIPTION does not exist”. Is this warning in response to the phone generated message?

In the end, the digium/Asterisk GUI display the phone or user as registered.