Hi Ruth,
If you meant the problem is INTERMITTENT; probably it's not a 7971 firmware issue. BTW., which firmware load do you have ? FYI., the latest one availbale for that IP Phone device model is 8.4(1)_Sr1. Kindly download and test it from here
http://tools.cisco.com/support/downloads/go/Redirect.x?mdfid=269065653 regards,
Ram