if this feature (contact form) is integrated in the Directory plugin, it would be a plus. Especially, the system can possibly count/record the "leads" that are sent from the directory to the business owners, so the admin of the Directory can charge the business owners for "Cost per Lead", as a complement to the "flat rate" subscription plan - for example, the listing is free, but the business owners will need to pay for each lead that is sent to them (as long as the contact information of the lead is valid - not spam).
Say, one business owner paid and signed up to list his/her business info in our WordPress Directory website, can he add a contact form right there on the listing page. So, the visitors (potential customers), while still on the listing page, can fill out the contacf form on that page to ask for something (quote, call back, inquiry, etc.) without login to his/her own email or going to the business owner's website to find the contact form there.
And the message will be emailed to the business owner's email directly. (so if we, the admin/webmaster, can keep a copy of the record, that would be sweeter, which can be used to charge the business owner - Cost per Lead, then, more money will be flowing in to WPMUDEV site, LOL )
David has suggested a plugin to do the contact form. Just thinking it would be nicer to have the contact form integrated with the directory and the payment system (to charge cost per lead).