Cellular

BitPim
Graphical manager for CDMA phones
http://www.bitpim.org/

bluexmms
Allows remote control of XMMS using a bluetooth-enabled SonyEricsson mobile phone, assuming you also have a bluetooth-capable laptop/computer.
http://linuxbrit.co.uk/bluexmms/

CUTs - Cellphone Unix Terminals
Enables you to use a normal cellphone as a Unix/Linux terminal from anywhere.
http://codewar.net/cuts/

Gammu
Mobile phone communication library, a command line application and a SMS daemon.
http://www.gammu.org/

Gammu phone database
Reports from users about mobile phones supported by Gammu library.
http://cihar.com/gammu/phonedb/

gnokii
gnokii (from GNU-Nokia) is a project to develop tools and drivers for Nokia mobile phones for Linux, BSD and other Unixes/operating systems.
http://gnokii.org/

gsmlib
This distribution includes a library to access GSM mobile phones through GSM modems. Features include: modification of phonebooks stored in the mobile phone or on the SIM card, reading and writing of SMS messages stored in the mobile phone, sending and reception of SMS messages.
http://www.pxh.de/fs/gsmlib/

KMobileTools
KDE-based application that allows to control mobile phones with your PC.
http://www.kmobiletools.org/

linuxsms
A script in Perl to send short messages to GSM phones.
http://linuxsms.sourceforge.net/

OpenOBEX
Free open source implementation of the Object Exchange (OBEX) protocol.
http://www.openobex.org/

OpenSync
A framework to synchronize PIM data between mobile devices like mobile phones, PDAs, desktop computer PIM tools and services.
http://www.opensync.org/

PhoneManager
A GNOME program to send and receive SMS messages through cell phone.
http://live.gnome.org/PhoneManager

SCMxx
A console program that allows you to exchange certain types of data with mobile phones made by Siemens.
http://www.hendrik-sattler.de/scmxx/

TuxMobil: Mobile Phones
Information about mobile (cell) phones working with Linux.
http://tuxmobil.org/phones_linux.html

Wammu
Graphical phone manager using Gammu as it's backend.
http://wammu.eu/