Sharon,
Unfortunately the CDMA technology utilized by Verizon Wireless (or at
least the typical US implementation of it) does not support that function.
I believe it is possible on GSM networks, so if you find yourself roaming
internationally you may be able to do it.
CDMA is capable of doing a 3-way call if the third party is an outgoing
call, but not incoming. The best you can do is utilize Call Waiting to
toggle between the two calls. If you hang up on the third call, your
phone should ring back (probably from an "unavailable" number) and you can
reconnect to the original party, and THEN start an outbound third call to
join them into a 3-way call. The ringback scenario probably varies by
market, but here in Richmond, VA that's how it works for me.
Steve