I have created a custom Contact form which is attached to the contacts. I
would like to use a button on the custom form to open the default Contacts
form with the Activities tab selected. The Click event would detach the
contact from the custom form, open the default form with the Activities tab
activated (which is what I don't know how to do), and then reattach the
contact to the custom form again leaving both forms open.

Right now, I can open a contact in the Custom form, click a button on the
custom form to detach the contact from the custom form, and then click on
the contact again which opens the default form leaving both the custom and
default forms open. But once the form is detached from the contact, it
remains detached until Outlook is restarted (which attaches the form to all
contacts) or a button on the main outlook toolbar is clicked attaching all
of the contacts to the custom form again.

As far as I know, the only way to get the functionality from the Activities
tab would be to either open the default contact form with that tab selected
or create another custom form and try to reproduce the functionality.

If possible, how can I open the default Contact form with the Activities tab
activated?

David