Is is possible to extract (e.g. into a formula) the "Type" of a Contact's "Last Activity"?

 

I'm using Pro edition.

 

thanks,

Tommy

I am trying to create a formula field as a number. What I need to do is work out the time difference between Now and a date on my custom object rounded up to the nearest month. This would be easy to do in code but I can't work out how to do it in the formula field.