Sounds exactly like the issues that we experienced. The phones would cut out and reboot on there own at random times and places. When running with the 184.108.40.206 version of the controller we had many unhappy users with our Spectralink i640 phones. Our solution was to downgrade to WLC 220.127.116.11. I believe that there is a version of 4.0 that is stable with the Spectralink phones, but I was unable to find the e-mail from TAC that had that version number in it. We decided to run the 3.2 version since TAC indicated that the 4.0 releases were Early Deployment builds and not General Deployment builds. One of our many frustrations of the WLC was no documentation indicating if a version was a ED or GD release. I have heard that 4.1 is supposed to be a GD release.
We spent three very frustrating weeks in production with a 4.0 version of code before we downgraded to 3.2. After we began running the 3.2 version of code, we were forced to reset the controllers to factory defaults and reconfigure them identically 4 or 5 times because the simply stopped working. Things have been stable and working well for the past 6 months mainly because I no longer make any changes using the WCS on the production controllers at all. Somehow the slight tweaking and tuning of the controllers kept breaking their functionality (specifically with windows 2000 laptops using Linksys WPC11 cards and with pocket PC devices). I now do all of my configuration through the CLI interface so that I can easily save a full list of the configuration settings in a text file. With the config files from the controller not being in a plain text format I don?t want to drag any ?garbage? along from a potentially bad config file.
I am hoping that 4.1 will be much more mature version of code. I am currently running it in a test environment.
I would make sure that you have 1,2, and 5 MBps enabled. Also, the latest version of code doesn't seem to have the same problems. We were running the same spectralinks with out an issue however the Nortel branded version had multiple problems.
Make sure your controller code is at least 18.104.22.168. Anything earlier does not understand the Platinum QOS level. If you cannot upgrade just change your QOS level to silver on your voice ssid. This advice is only assuming a similar issue I had. Hope this helps.