Hi,
There is no way to do this with OCS natively; there's no support for hunt groups and you can't assign the same number to users in OCS.
You could possibly look at writing an MS Speech Server application to simulate a hunt group, or you could just use one user/number and have a few people sign in as that user. The trouble with that is if one user is on the phone, then the number is tied up and no new calls will route to the other people logged in as that user.
Until OCS supports hunt groups you won't really be able to do this.
Regards,
Matt