I think where I changed mine was on the OBiTalk web portal. Go under expert configuration, then go under voice service, click on the SPn that you want to change, uncheck both default and Obitalk boxes next to Display Label and Display Number and enter what you want it to be. (When you uncheck the ObiTalk box, default will automatically become checked and you will need to uncheck it too before you can type in the fields.)