Am I able to use 18866 if I am already registered with Alpha or Onetel?
Yes, you can. If you normally dial another Indirect Access code before your calls (for example 1833 for Alpha telecom or 1877 for Onetel) you simply omit this code and just dial 18866 or 0808 1 701 701 instead.
If you are using a router box (also known as Phone.Pal) you can either unplug the router box or dial 1-2-1 (or whichever override code is provided by your service provider) to bypass your router box followed by 18866.
Should you have chosen to have all your calls automatically routed through another provider (also known as Carrier Pre-Select or CPS) you will still be able to use 18866 as usual. Just sign up and dial 18866 followed by the telephone number to make cheaper calls! Your CPS provider will not charge you for dialling the 18866 code, therefore the 18866 code will not appear on your CPS bill and any calls made using the 18866 code will only be invoiced by Call18866.