From Longman Business Dictionary
SMSSMS nounCOMPUTINGTELECOMMUNICATIONS1[uncountableU] (short message service) a system for sending short written messages between mobile phones 2[countableC] a message that is sent using SMSBank customers will immediately receive an SMS to verify their transaction.
—SMS verb [intransitiveI, transitiveT]We will also SMS you if we have any new midweek buy or sell opportunities.