How do SMS services work?

Question

API

Good evening.
There are many services for receiving SMS online.

Give-sms.com | SmmMonster.com | GetSMS.online | 
Sms-activate.ru | 5sim.net | Smska.net | SimSMS.org | 
Sms-get.co | BySim.ru | Sms-acktiwator.ru

How can I get SMS text on a computer / server with a SIM card? I doubt that these services have hundreds of phones connected to the computer. Most likely there is some kind of universal tool (into which the SIM is inserted) to activate the SIM card and receive SMS through it? Or is there some big number reseller?

Answer 1

2 universal tools:
1. Direct contract with the operator to whose number base they receive SMS, with the connection of their SMSC via the SS7 channel. If there are hundreds of numbers, be sure that this "tool" is used.
2. GSM gateway . If there are not many numbers, this solution is much cheaper and deploys faster.

Answer 2

SIM-banks are used. For example like this .

Answer 3

depends on the size of
those that are SMS billings - those as @SyavaSyava wrote,
but there are also basement