Have a family member who has a Samsung Note on T-Mobile. She and I both text quite a few others on different services but occasionally, like today, my text to her will not send, just sits in my app telling me it didn't go. There is an option below that that says I can try SMS/MMS (I think) and occasionally that will work. I have also found that if I disconnect from my work Wifi then it will send. But then I will get an email a few hours later asking if I got their text messages which I didn't. Then I switch from wireless data back to my work Wifi and all their text messages come in. I text with dozens of co-workers and other family and this one T-Mobile account is the only one I have issues with.
Any clue what to look at?