The main department phone number is 512-471-7316.
The CS Department maintains its own phone server. Operating phones in CS is similar to elsewhere on campus, but any questions or problems should be sent to helpreq@cs.utexas.edu.
To call an on-campus number, simply dial the 5-digit phone number. For off-campus local calls, you'll need to dial 9-512-XXX-XXXX. For long distance and international numbers, you'll need to obtain a 6-digit long-distance dialing code, and then dial 8, wait for a dial tone, enter your long-distance code, wait for another tone, and then enter the number you're dialing (either 1-XXX-XXX-XXXX for US/Canada or 011-[countrycode]-[areacode]-[number] for international calls.
To access your voicemail from your phone, dial *512 and enter your password when prompted. You'll be given a default password when you start, but you can change that in the voicemail menu. If you need your voicemail password reset, send mail to helpreq@cs.utexas.edu.
To enable call forwarding from your phone, dial *72 and follow the prompts. To disable it, dial *73.
For a directory of CS numbers, dial 411.
For emergencies, dial 911.