Phone Verification Question

I am building a website which requires phone verification from all members in order to create an account. As I understand, the Carrier(AT&T, Verizon etc..) and whether it is a Mobile, Landline or VOIP number can be determined. What I want to do is to only allow an account to be created if they are using a major Carrier such as AT&T and only either a Mobile or Landline number. What I would like to know is if there is any easy way for someone to purchase a lot of phone numbers in order to create multiple accounts if I am not allowing VOIP numbers to be used for phone verification?