Do you already have the UCL and CUWL? 7.1.5 and above for the new licensing. I belive after you upgrade you just add the new license file and it will convert the dlu's to the new system so if you have 500 ip phones and 3000 dlu's I believe it would just switch back to 500 UCL/CUWL or how every many you bought.
If you have smartnet I would call them up and ask to be 100% sure since its new and not a real requirement until 9.0 I dont know if many will be doing it. Though they do have a great deal on converting from DLU's to get people to switch over.