I have a Samsung phone and for two days I can't send or receive text messages on it. It worked totally fine and than all of the sudden it kept on saying sending failed. And when somebody trust to text me it says invalid number even though I just was texting back and forth with that person.
BellMTS Tech support is open today and may not be to busy if you want to call them @ 204-call-mts (204-225-5687).
One question before you call BellMTS support is do you know if the other people you are have having problems texting with are also BellMTS customers? If they are not on BellMTS then the problem may be at the other cell company.
Also if you have not done so try turning off your cell phone for about 30 seconds and turn it back on. If for some reason it lost contract with the text part of network this may reconnect it.