This page describes the plans to develop Plasma Mobile from a high-level. Day-to-day development and planning is done in KDE's Phabricator system.
The Plasma Mobile prototype shows the viability of Plasma on a handheld device. The prototype boots a reference device, is able to make phone calls, select contacts from an address book and contains partly functional outlook on how handset running Plasma could look like.
Plasma Mobile 1.0 provides an end-user ready experience with a minimal, useful feature set. This includes the underlying OS and plumbing layers, a workspace to launch and manage apps, some basic system functions to set up the network, show connection status, etc. The feature set for Plasma Mobile 1.0 is described in this phabricator workboard.