You're probably getting an "IP Flex" service, which combines Internet access with the voice service. Telepacific knows how to do 5ESS, be aware that you don't get Name, only Number. They will insist on sending you 4 digits, so you will need to read up on PRI routing tables. And you will need them to send your main number on all outgoing calls, the Legend will send invalid CID for extensions that don't have DID numbers.
Finally, if you are using T/R ports for Faxes or modems, expect them to fail!! You might want to keep them on POTS lines, and if you remotely access the Legend for programming, that also will not work over the IP Flex.