Custom CS Numbers allow you to get a permanent (or as long as you want) number assigned to your phone. You can get text messages and phone calls on this number without you having to register the phone number of the person you are expecting a call/text from.
It is basically like getting a 2nd phone line. You can get as many Custom CS Numbers as you want.
Calling/Texing using Custom CS Numbers
Once you pay for and get a Custom CS Number, you will see a new selector on the app home page that allows you to pick the number you want to use for the next phone or text message you send. Pick the number you want to use, and dial/text as usual.
Note that once you have dialed/texted a person using a CS Number (Custom or Randomly Assigned), whenever you call that person, the same CS number will be use every time. This will happen even if you select a different Custom CS number. If you really want to call the same person using a different number (Custom or Randomly Assigned), go to the 'Dialed' menu and 'delete forever' that person's number. Then come back to the main screen to pick the CS number you want to use for subsequent calls/texts to that person.
Custom CS Numbers are renewed automatically a few hours before they are about to expire. You must have enough funds in your account to cover the renewal. If you do not have enough funds, the number will automatically expire. Note that once a number expires you cannot get it back. So make sure you pay attention to the renewal notice that is sent about 24 hours before the number is set to expire.
You can cancel a Custom CS Number at any time by going to the Menu > Manage Custom Numbers, then click on Manage my Custom Numbers button. Long press the number you want to delete and confirm.