Hi Shelley,
From your post I understand that you want to place a 'Send email' button adjacent to the 'Email' field under the Customer List, in the Address Info tab section, correct?
When you click on the 'Send email' do you want the Add/Edit Activity screen to pop up? This is the same screen that pops up under the Activities tab section when you click on New Activity.. button. The reason I'm asking you this is because if you just click on Send email from the Address Info tab section then how are you going to fill in the body of the email, select the option to choose a template, etc?
Perhaps you can try adding a button that would show the Add/Edit Activity screen in a pop up. Also you can move the 'Send an Email' tab section up so it's the first tab section the user sees and they can fill out the information accordingly. In essence, you'll be moving the 'New Activity...' button to the Address Info tab section and then modifying the 'Add /Edit Activity' screen. Please let me know if this is what you're looking for.