We have a master list of over 600,000 records in Marketing Cloud (ExactTarget) that was not set up with a Subscriber Key. As we're planning on using SMS for some subscribers, we need to set up a unique subscriber key for everyone on the list. We don't have (and don't need) mobile numbers for everyone so that isn't an option.
As an added twist, we have 4 different platforms adding subscribers to the list.
Is there a way to generate a unique subscriber key automatically for new records, or will we need to create some sort of web service that generates a key and call that from each platform when adding a new record?