code: func (ipn *IncomingNumberService) BuyNumber(phoneNumber string) (*IncomingPhoneNumber, error) {
  	data := url.Values{"PhoneNumber": []string{phoneNumber}}
  	return ipn.NumberPurchasingService.Create(context.Background(), data)
  }
docs: // BuyNumber attempts to buy the provided phoneNumber and returns it if
  // successful.