We're a hospital with high availability wireless requirement, including Vocera VoIP communicator badges. We want to upgrade to new 3502 APs but first need to migrate 8 production 4402 WLCs all in the same Layer 2 mobility group from 4.2.61 to 7.0.98 which requires 3 reboots (2 step version upgrade plus boot code upgrade). Can we temporarily mix different WLC versions during the upgrade process within the same mobility group without totally blowing up our very stable wireless environment? I want to upgrade one WLC at a time after first moving the access points (one at a time) to an upgraded controller so as make the upgrade of our 170 LAP1121 AP's as transparent as possible to our users. I already have two additional spare WLC 4402s running the 7.0.98 code but I have them defined with a different mobility group name. I'm having VERY intermittent, infrequent Vocera VoIP call establishment issues when trying to connect badges across the different mobility groups, so I'm thinking I might have better luck if I just put them all in the same mobility group during the upgrade though I understand the cross-version isn't supported. Will different version within the same mobility group work for the two or three days that I anticipate this upgrade will take, or am I playing with fire? Thanks!