This is an important stage for device creators and developers, but is not of major significance to consumers, other than to indicate that Symbian^3 is well on track for being in devices in the second half of the year. The Nokia N8 was the first Symbian^3 device to be announced, but there are many more on the way from multiple manufacturers.
What does functionally complete mean?
Functionally complete means that the Symbian Foundation Release Council believes the release is at the point at which it is ready for the community to start 'using' and hardening it. It does not mean that the release is feature complete as there could still be minor changes.
'Using' it could involve developing devices, creating apps, or evaluating the capabilities and performance of the release. The release now moves into the hardening stage - this is the process of getting the release ready for use in consumer devices. For Symbian^3 development the focus now shifts from adding features to improving stability, fixing defects (bugs) and related activities.
In terms of SDK releases for Symbian^3, a technology preview (alpha) is expected later in June, the functionally complete version (beta) is expected in August and the hardened (full) release is expected in October. PDKs for Symbian^3, which are targeted at device developers and platform contributors, are already available.
More information is available in the latest Symbian Foundation release plan PDF document.