This is how my scenario works: our customer service will use our own CRM press the CALL button to call the customer, customer service are don't know customer's phone number, have to call via our CRM. After customer service gets in touch with client, customer service will request client to enter the credit card number after sound "beep", and the client will enter the credit card number via their phone number pad, and after client enters the credit card number, the credit card number will save into our CRM system.
What kind of VoIP or PBX do I have to use? Any solution? I have no idea about this.
In Voip when SIP is used, you can have a proxy server / sip server /b2bua which connects the customer service and client. After that when client specifies the digitis, it can be received 1. as SIP Info message 2. As part of RTP
For the first case you can read those message in the proxy server / sip server /b2bua and feed it CRM without reaching the customer service. But for seconds case you have to have an media server which processes the media in between customer service and client which can add data to CRM without sending it to client.
I hope I provided one solution to your problem