Switching is easier than ever now that Google has created some pretty nice iOS apps for all of their services. Even if you are embedded deeply into their ecosystem, you should be able to access all of your data fairly quickly if you're making the switch to iPhone (download the apps, login, and go). Then over time you can decide what data, if any, you'd like to move to Apple or 3rd party services.
The same is not true when moving from iOS to any other operating system. Which, of course, is intentional.
The same is not true when moving from iOS to any other operating system. Which, of course, is intentional.