May be a settings issue or a carrier issue (Does your mobile carrier allow mass sms? if so check your sms settings themselves. I have no issue sending mass messages on the a70 or the S10....
Must of changed just when ever i changed my number and tried to send it to all my contact it would only lwt me send 10 its strange how they work it u wud think u could send 1000 at a yime if u wanted to as we pay for out sim card