We know one of the benefits of ivolunteer.com is email verification of users without a formal username/password. Is it possible to have volunteers create a login with contact information?
When a volunteer signs up for the first time (or the Administrator signs up a volunteer on their behalf) the confirmation email contains a unique link through which that volunteer can access his or her volunteer commitments (and cancel a commitment if you allow self-cancellation). Whenever a volunteer signs up or receives a reminder, that link would typically be included again in that email. A volunteer can also re-send themselves that link by visiting any event they have signed up for.
Your administrator(s) could also create a “registration” event with Custom Prompts for additional information such as address and phone number. You could then either ask your volunteers to sign up using the “Registration Event.” This information can be linked to and viewed in the Organization’s Database, where you can group volunteers and send out emails to the entire Database.