i recently did a 4-5 digit conversion using Provision myself for a 6,000 station switch, 5,000 agents & 820 vectors. Using excel and formula's, the manipulation of digits was the easy part. The hardest part was going into each station & vector to check if any 4-digit references existed. That was probalby the largest undertaking with the most room for error.
The stations i could deal with when loading everythign with Provision, because i could see the errors and then go back and fix the file where there were mistakes. But the vectors would only tell you where collect digits & announcement statements were wrong, not the route-to's so those had to be fixed manually and looked at a few times. I had a surrogate 8700 server in my house that i used to load the translations and build essentially a translation (xln) file and after i was done, i took the translation card, on the night of cutover, put it into the 8700, did a restore of that file, then did a "drestart 1 4" command and it brought everythign back.
First day issues were minimal really on the pbx side and definitely not big that couldn't be fixed. Call Center worked great and just little station issues had to be fixed.
It was probably the biggest undertaking i've done but it was a short time frame and we met it really well. It probably took a total of 30 hours with the Provision work on this. 3 full days of me and my counterpart goign thru the vectors & stations, which i had to look over anyway before importing.
So, it can be done.