Mine sends MMS when I'm on the WiFi. You need to have a good T-Mobile signal for any text to send as texts don't send over WiFi at all. So if you're in the middle of an all brick building and have no T-Mobile signal but full bars on your WiFi so you can still call out, then yes you won't be able to text.

If you want to text over WiFi then I suggest you get Google Hangouts and urge your friends to do the same.

 

That is odd, very odd. Mine sends texts, MMS, makes calls no problem with Wi-Fi on. If I'm on Wi-Fi when browsing and I walk out of range of the signal it switches to network (LTE, HSPDA, whatever) easily. If a page happens to be loading/rendering or I'm streaming it very briefly (half second max) stops and then restarts. If going from Network to Wi-Fi it waits until I've either finished streaming or the page I want to view renders, then switches to Wi-Fi.

There are more than a few examples of weird connectivity problems and they all appear to be non international variants, particularly US models. Correlation perhaps?

 

Try going into the Wi-Fi calling menu and changing it to celular prefered. I had issues with calls and texts over Wi-Fi and that fixed it for me. The pictures I'm not sure of. I'm pretty happy with the camera. It takes pretty sweet pictures for me

 

As I said, odd. It might be worth a shot requesting the settings for mobile internet and MMS from your carrier (network). They'll send you two SMS, open them and save them when requested to, at least then you'll have their correct settings for sure.

 

When I had my Galaxy S2 a while back, I couldn't understand why my phone wouldn't receive MMS until I realised that mobile data had to be switched on, even though I was on Wi Fi it would have never received.