How to allow non-registered users to email sellers?

[mattbaxter]

I kow I might be opening up doors for spambots, but i am keen to take that risk as a test.
At the moment if a product price is blank there is an option to contact the seller by email.  The button is named 'Call for price'.
I have a lot of shoppers that would rather stay off the radar and might not be keen to register.  So they are blocked from emailing the seller.  Is there a quick and easy way to allow this to happen.  Have looked at the config and there was no apparent setting.

[jenkinhill]

VM Configuration/Shopfront/Recommend a product, ask questions  - turn on  "Allow non logged-in to send a recommendation or ask a question"