Did you raise this at mailchimp via support or your account manager?
As the others pointed out, you could somehow work around it using dummy email addresses (and at least get this approach approved by them since they don't have the SMS-only feature yet).
Maybe you could create aliases using "+" in the email addresses and use one of your company inboxes/addresses for that matter.

Otherwise, you'd want to switch to a different provider for SMS and keep them in sync or move with mailchimp once you also get their email.