iMessage Problem:Software or Hardware

So basically like the thousands of other users, my iMessage is down for my phone number after upgrading to IOS 7 on my Iphone 4. The main problem is that not everyone has send as SMS option turned on so lots of iMessages sent to me are stuck in iMessage purgatory--sent but not received.

I've tried resetting my network settings and everything but to no avail. Since I'm still using my Iphone 4 and it is on its last leg of life, I am considering buying the new Iphone 5s BUT here is my question:

Is iMessage a hardware problem? Like if I buy the new iPhone 5s, will it automatically be fixed

or

Is iMessage a software problem meaning that if I got a new phone, I still have to wait for the bug to be fixed.

 

Well my iPhone is unlocked via an eBay unlock to work for T-Mobile. I tried resetting my network settings and immediately after that, my phone could only call and couldn't text at all. Luckily that same day Apple released the new IOS 7 update and that was able to fix the texting problem.

Im just really cautious now when it comes to restoring network settings and everything along that line now