There are many free bridge lines out there and the one that we use and highly recommend is FreeConferenceCall.

Once registered, you'll receive a dial-in number, access code for participants, moderator code for your use and other account details. Record the information in the printed checklist.

I use one bridge line for each virtual event that I host. When providing information later for your participants to call in, they only need the dial-in number and the access code.