Samsung Galaxy 4 does not receive text message from iPhone.
This was a known problem and it only applies if you change from an iPhone to the Samsung Galaxy S4. To deal with this problem, simply use the iPhone, then go to Settings > iMessage > Turn off or go to https://supportprofile.apple.com/MySupportProfile.do and unlink your iPhone, then you can receive messages on the Galaxy S4.
There is also a troubleshooting page you can use for this purpose: https://support.apple.com/en-us/HT204270
