how to send group texts

I am using an iPhone 4. I am with T-mobile and have their unlimited plans for all data, text and calls. I am able to send texts to single recepients without any problems regardless if they use an iphone or not. Not long ago I was able to send out group texts containing as many as 26 contacts in the receipients list. I was able to get my texts and my replies to show up on all of my Apple devices which included; my MBP,iPhone 4 and iPad 2. I recently noticed that i am no longer able to send out a text containing more than 3 reciepients. I recently added an app from the iTunes app store called "Text to Group" . It does seem to allow me to send out texts to multiple recepients, but It requires me to turn off my imessage. When I do, I am no longer am able to see the text messages my other devices. It requires me to only use my iPhone to send and receive the replies.

Is there a way for me to send out group texts and still be able to view the message and the replies on all of my devices?