First I'd recommend that you upgrade to 7.1(3) - specifically 7.1(3b)SU2 and not 7.1(2). Unless of course, you've seen all the bugs and are OK with them.
Upgrade firmware in advance of the migration. Trust me, this will save you a headache.
Clean up everything in the DMA file. Even the the little stuff.
If you have Unity, check the TSP firmware version for compatibility. You need to be at TSP 8.1(3) or higher for 7.1 compatibility.
Upgrade the Publisher first, then TFTP server(s). From there upgrade backup subscribers and swing phones on to them. Lastly upgrade your primary subscribers and then phones will re-register as expected.
On a final note, understand the new CFA CSS activation policy and how it may or may not affect your environment - be prepared for it in advance. Read this blog: http://www.netcraftsmen.net/resources/blogs/cfa-css-activation-policy-what-it-is-how-it-works-and-why-you-need-to-know.html
Hailey
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