IPhone won't receive group texts from non-iPhones?

My iPhone won't receive any group chats if someone else in the group doesn't have an iPhone. Why is this and how can I fix things so I receive group texts from all kinds of phones?

When everyone has an iPhone, the group texts can be managed entirely by iMessage. If anyone does not have an iPhone, the messages will be sent via cellular SMS or MMS, and not everyone will receive all replies. Many other smartphones are not capable of handling group texts, and only iPhones can do so with iMessage.