How many different numbers you are having and what is the price for bulk purchases like 100 or 200 SMS verification services.
Will you be able to offer this service for other than facebook and gmail like for some gambling sites or for Uber app verification ?
If you need new numbers for Uber app registrations, I believe I can provide up to 10 numbers internationally (my numbers and my friends' number). But you can not expect big discount for this as I have lot of background works need to be done for this.
(Sorry OP for offering this here, I see you offering professional service, mine is not so)