What is the fastest SMS gateway for SMS registration?

Question

SMS

The question is for those who really used, and did not read other articles, advertisements or reviews.
SMS mailing is not planned, but only targeted for registration. It is necessary that the interval is no more than 10 seconds at least.
ps We used the services (although the package still remains) of one such operator. At first, the delay was ~ 12 seconds, and then increased to minutes.