I used to have an iphone and recently moved to Android. I now have a Nexus 4 and a Nexus 7 and I'm extremely happy. However, I do miss one feature of my old iPhone: iMessage.
Is there a replacement app for messaging that can be used both on a phone and a tablet?

Have you tried Whatsapp or Line? Both of them are good.

Can WhatsApp be used on both - tablet and phone?