I have 2 fields in my table, one named Contacts and the other named Need to Contact. On my form if I choose Contacted (making the value yes) then I want the control Need to Contact to be dimmed out so that the user can't enter both. Maybe with error message saying you have already contacted this person. User can't choose both! In other words. If user checks off Need to Contact and Contacted has not been checked then choosing Contacted should be able to be checked. Hope this makes sense.
Maybe consider making the 'contacted' a date, not a Boolean, and make the 'NeedToContact' a function of the 'contacted' date plus some constant, such as 6 months.
In other words, the user would enter the last date contacted ('contacted'). This should make 'NeedToContract' equal False. In 6 months, make the 'NeedToContact' True*, so that a report, perhaps 'Print out all Customers With NeedToContact' would print out the customers that should be contacted.
*This could be done in a macro/VBA event that runs every day when the database is opened for the first time.