Most of the EDT emulation commands are keypad keys, and most standard Emacs key bindings are still available. The EDT emulation rebindings are done in the global keymap, so there is no problem switching buffers or major modes while in EDT emulation.
Viper is the newest emulator for vi.
Because vi emulation works through major modes, it does not work to switch buffers during emulation. Return to normal Emacs first. If you plan to use vi emulation much, you probably want to bind a key to the vi-mode command. To get from emulated vi command mode back to ordinary Emacs, type C-z . This emulation does not work through major modes, and it is possible to switch buffers in various ways within the emulator.