Thank you very much for your comment and my apologies for the very late reply.
My system is similar to Evan’s. If I want to follow up with someone I create a task in the @Contact folder, link it to the contact of the person I want to follow up with and assign a due date. The task/reminder then pops up automatically in 2Do on the due date I assigned, showing the person’s email, phone number or address depending on the manner of contact I have specified in 2Do.
2Do syncs with the contacts from the iPhone phonebook, which in turn syncs with my Gmail contacts. It doesn’t sync with Google calendar or the iPhone calendar, though, and the developers have made it clear that they see task management as separate from scheduling appointments and won’t implement calendar sync (I understand that limited sync with iCal is possible but I’m on Windows so I’m afraid I don’t know many details).
I hope that was helpful. :)