Personal Digital Assistants (PDAs) act as personal organisers. PDAs have many uses: calculating, use as a clock and calendar, playing computer games, accessing the Internet, sending and receiving E-mails, use as a radio or stereo, video recording, recording notes, use as an address book, and use as a spreadsheet.
A smartphone or sphone is any electronic handheld device that integrates the functionality of a mobile phone, personal digital assistant (PDA) or other information appliance.
A Pocket PC, abbreviated P/PC or PPC, is a handheld-sized computer that runs a specific version of the Windows CE operating system. It has many of the capabilities of modern desktop PCs.
A mobile phone is just an ordinary phone.