What is the process to convert a database that is 3.0 to 3.5?

The procedure is in the 3.5 installation manual under maintenance and troubleshooting...Flash ROM Update. It requires a lot of steps and some passwords, so it is better we don't put it here.

I would take your system to 4.0 (do not use 4.1) which allows the XTS to use some of the newer phone sets, like the Edge 700 series.

Thanks for the input. I ended up loading the 3.0 backup that I had using Procomm into the new MPB1 with 3.5 and I worked fine. I installed the new MPB1 last Friday and did some test calls and everything seemed OK. The customer has not called about any small problems. Now I'm waiting to find out if it resolved my problem with the IP phones when conferenced.