Customer has mobile number only, no email ID

I have a question on Marketo and would like your expert opinion on the same -
We have only mobile number of the customers and would like to use Marketo for SMS, whatsapp, push and in-app. We do not want to capture email ID of the customer, and work with mobile number only?

What are the challenges in this case? Can I make mobile no. as primary ID for dedupe? Will it work in similar way like email ID?  How can we circumvent the email ID requirement of Marketo to deduplicate customer records? Any issues which you foresee? Your insights will be really helpful for us to make the prospect aware of the limitation and issues they can encounter