Doing it that way will only change the extension number but won't assign features, lines, hunt groups, ring groups, answer DNs, etc that are currently on the digital sets. What I do is unplug the digital set, wait for a few minutes and keep refreshing the Element Mgr Active Sets page until the digital sets no longer show up as active (calling the extension a seems to speed this up, when it says "inactive" you're ready - takes 5 minutes or so.) While you're waiting you can be preparing the IP set. When the IP set requests a new DN, you can just assign the DN of the digital set you unplugged if it is shown as inactive in EM. All the line assignments, hunt groups, ring groups, answer DNs, etc and most button assignments will be transferred to the IP set. Some buttons i.e. the message button may need to be reprogrammed as the key locations don't exactly allign with the digtal sets. Using this procedure I've been able to replace 8-10 sets in less than an hour with no mistakes.