The closest place to buy a phone and/or register a SIM card is in the local post office.
They offer a "Golan Telecom" companys' SIM card and plan for 16 NIS/month. Pay attention that phone companies require a credit card. So it's better to do this AFTER you get your Israeli bank account.
The plan offers 3000 texts, 11 gigabytes, 3000 minutes of domestic calls and 60 minutes of international calls (not all countries).
It will cost 19 NIS for the SIM card + 11.7 NIS commision for SIM activation + 16 NIS for the monthly pack.
For activation you need to call this number with an Israeli phone number (find a friend or lab mate that can spare a call). Representatives speak Hebrew and English.
Another option is in stores in Beer Sheva. In order to do so, you need to have a passport and a credit card. Below is a list of stores that students have used in the past and some information on mobile plans in Israel.
Beer Sheva Canyon Mall: BUG store (Golan), Orange
All of Israel's major cell phone carriers offer reliable service in the Midrasha. While plans and special offers change periodically, you can check out the latest on their websites:
Additional information/tips about getting cellphones in Israel can be found here.