Orientation
Orientation is frankly a bit of a pain. So let's make it simple. You either handle orientation or you don't. The simple solution is to display your app in portrait unless you really need to display parts of your app in a landscape format.
Restricting the orientation
The problem with allowing orientation for some parts of your app is that you have to handle the transitions. For example, suppose you have two tabs; on one tab is a picture that you need to show in landscape, but on the other tab you have a form in portrait. The users look at the picture and rotate the phone to landscape. They then change tabs, without rotating the phone. What happens now? Should the app show the form in portrait? Or will it show the form in landscape?
Both circumstances are hardly ideal and both could happen; your form could appear in landscape or the app could rotate for portrait, annoying the user.
The simple solution is to create a portrait layout for phones and restrict the orientations in tiapp...