I haven't even considered anything like this because i'm on my iPhone almost approximately 90% of the time. .....I would definitely have to give this some thought. Good question, by the way...
Momento app for ipad
Whatsapp app for ipad
Viber app for ipad
Carrier SMS and phone call app for Sim enable ipad (not talking about voice over ip application)
I have half the apps on my iPad as I do on my phone and only of they are built for iPad for my convienence and ease of use like my banking app and a few others.
I have about 50 on my phone and half as I stated on the iPad.