[annaba1]

My sister, mom, and I all have iPhones. Running iOS 6. All of us have imessage activated but most of the time our texts to each other sense as SMS. Me and and mom normally get imessage. Sometimes we don't though. But with my sister it's ALWAYS SMS. Any tips? And yes, again, imessage is activated.

[Massie]

You can activate it using a few different methods: phone number, email address, etc. Make sure that the contact info for your sister is the same contact info she used to set it up.