Having been involved in the telecoms industry and in particular the sms industry for a number of years I can tell you that it is very much a game of cat + mouse for most legit bulk sms providers, aggregators telcos (the cat) and the illegit mice (the spammers). Unortunately spammers will always be around whether or not they use SMS or VOIP or in the old days snail mail (anyone remember the 100's of unsolicited advertising envelopes the poor old postman used to deliver?). Telcos have been trying to block it for years (since sms took off) with sophisticated spam filters plugged in to their networks as well as DND (Do Not Disturb) etc etc etc. This costs big numbers to integrate and works well till the spammers find a work around. Sim farms with thousands of rotaing sim cards look like P2P (Person to Person) legit texts plus numerous other ways including modems and the list goes on and on of circumventing even the best deterrents. Ultimately the only safe way to avoid sms spam or voip spam or nucience calls is not to have a phone at all.