If you're following a public-cloud strategy, the situation is a bit different: your entire objective is to avoid having to take ownership of (or responsibility for) most (if not all) of the services you're using.

Public cloud freeware apps usually start with limited functionality in the totally free version. Within a few quarters, it's typical to see some sort of advertising or sponsorship model added to the UI. (I have yet to see an advertising model added to a SOAP or JSON API, but somebody will devise one soon enough.)

Usually, the pay wall is erected a few months later, in the form of an unrestricted version that enables additional features or higher usage levels of the app or service. In most cases, the freeware is still available and isn't explicitly changed. (However, I have recently seen examples where the freeware is literally turned off or put into read-only mode, rendering it essentially useless.) In order to justify the price for the "full up" version, vendors typically add enough new features that the original user experience and APIs are obsoleted. At the very least, you'll need to do some testing.