[eeyore6802]

If you have 2 iphone users(regardless of what type of email accounts they may have) is there anyway either with the iphone calendar or a calendar app to send invites to eachother?

[fabuloso]

The same should still apply to your question:

Source: Apple - Support - Discussions - iPhone 3G sending calendar invites ...

Apple does not comment on future products or features (or complaints).

From the iPhone 3G manual:

"If you have a Microsoft Exchange account set up on iPhone with Calendars enabled,
you can receive and respond to meeting invitations from people in your organization.
When you receive an invitation, the meeting appears in your calendar with a dotted
line around it. The icon in the lower-right corner of the screen indicates the total
number of new invitations you have, as does the Calendar icon on the Home screen."

And:

"Tap Accept, Maybe, or Decline."

This means that answering invitations should work if you are connected to a Microsoft Exchange server.

It does not work if you're using MobileMe, because MobileMe is only "Exchange for the rest of us". And it does not work if you only use iCal with no server support. In short, if you are using iCal, you're out of luck.

Even if you use MS Exchange, you could only respond to invitations. You can't create them.

There's more. If you view an event on your iPhone, you can see the names of the attendees. You cannot see if they accepted the invitation because there is no status symbol. You can't see if you accepted yourself.

Have fun!