I switched to Simyo some months ago, and while I can use the internet, make calls, and even receive text messages just fine, I'm not able to send messages at all when I disable RCS chats (my most common recipient is very rarely connected to the internet, so using RCS is not an option).
I've already tried stuff like restarting my phone, clearing the message caches (both Android and Google messages), enabling and disabling airplane mode to force reconnection, updating my phone, updating the messaging apps, verified that the numbers are correct and not blocked, as well as resetting the APN.Â
While I neither get a confirmation that the message has been sent, nor of course does the recipient see the message, I do however see the 7 cent charge on my invoice for each individual message when the recipient is a foreign number.