Checking the Sim List for Validity?

Question

Skype

The question arose:
How to correctly check the list of numbers of my clients for on / off (validity).
there are several theoretical solutions:
1. by calling sip accounts - but account brokers can ban these accounts for supposedly "flooding" (although I need to make one call to one number within a second (waiting or not) - the same second))
2. via Skype - everything is very expensive here and there can definitely be slippage.
3. via modem - not suitable due to one stream.
(something tells me that I will come to the vulture)
Help me solve the problem)
thanks in advance.

Answer 1

SIP operators usually consider multiple calls to the same number as a flood. According to the experience of the year before last, I can say that zadarma bans outgoing calls to the number after the 20th zone for one number. There was a practice of calling via sipnet - several series on a list of several thousand - a ban was received only for launching several streams from one account and they called the same number - that is, they are punished for DOS of a remote subscriber.
If you need a more reliable service - a city number under an agreement from an operator that provides landing via SIP. in this case, the operator has no right to do anything with the traffic until subscribers complain (but you are doing an honest thing, right?)