no the number has to be vacant, so you usually need to null the key then go back and make the change.. the up side is when set a answers a call, sets b and c will still ring on the same number and each of them can answer before that dn is busy.. the down side is set a put the call on hold set b can't pick it up.. set a would need to use the transfer..
users tend to resist change but they get used to it and then it works much better
john poole
bellsouth business
columbia,sc