Hello sir,
I can make this work with warranty.
I'm Spanish, I have native Spanish people for the job too.
We can do it, with skype account or phone calls (if they are called in Spain) as you want, but always calls from one phone to another phone are better, because they generate customer confidence. Skype calls do not get the phone number for the customer (but it´s well)
I wonder what would happen if not contacted your customer, do I still would pay for the call?
Please contact me, because this job would give you total satisfaction.
(If you want we can talk in Spanish)
Regards!