My phone redirects such messages to the spam folder and lets me know. Not a big deal for me because at any one time I don't have much on order, and that small amount is easy to keep track of. A busier person might have problems.
As things stand, a perp might send 100000 free emails (using a program, so no time or work involved) and get 100 bites at £1.57 apiece. Since there is no way to report smishing, thus no way for the authorities to know the size of the problem, reports of the theft of £1.57 will have a very low priority. Until a cabinet minister gets turned over a few times, it will be a safe way to steal small amounts.