For example, will lawyers use China Mobile to send you messages?

Generally, it is made in written form, but personally, if it can be proved that the other party has received the short message sent by the lawyer, including the short message that the other party acknowledges receiving the relevant content, it can play the role of notification. But in reality, if the lawyer's letter is sent by SMS, it is generally difficult to prove that the other party has received it, that is, it cannot play the role of a lawyer's letter.