Yes, telco has to do it. System cannot control how telco routes incoming calls. So, one has to ask telco to setup an hunt group, and define which addtional lines it will re-hunt calls. Depedning on situation these line can be incoming only, or bidirectional. In this case, special care must be give to the CO and system hunt scheme to minimize glare.
Also, please note if using a bunch of analog lines like you're planning, that will not get the best results to the users, like fast dialing, immedaite CLID display, automatic hunt as described above, DID service, digital voice quality, etc. For best results, one should only use ISDN PRI, or SIP trunk.
Finally, but very important: unless you have significant amount of expereince with telephony and netwrok, it is strongly recommened that for sure and quick results you get an UC certfied Cisco partner, or person of equivalente knowledge and expereince.
