Is there a cost effective way getting a data connection (sim card) for a mobile phone for 3 weeks while I am in Israel? So that I can read emails, and make use of google maps on my phone?
Since the current answers are rather outdated, here's a web site with recent-enough information.
Generally, the no-contract plans are affordable. For example, Golan Telecom doesn't require Israeli identification documents, and you can even pay with a PayPal account. Their activation fee is 49 ILS, and for unlimited calls and 1GB data you'd pay 37 ILS monthly (59 ILS monthly for 6GB).
If you're staying for more than a month, getting a no-contract plan is the obvious choice.
The only difficulty is that low-cost operator SIMs should be either pre-ordered online (to an Israeli address) or purchased at one of their points of sale. Unfortunately there are no such points of sale at the Ben Gurion Airport, but you can find them in major malls. Check carriers' web pages for points of sale, e.g.:
Pre paid cards data connection in Israel can be quite expensive (in my opinion at least). From what I've seen on Orange BigTalk's website (sadly available in Hebrew, Russian and Arabic languages only), data connection on pre paid SIM costs are: 1MB = 4 NIS.
You can get those cards in Israel post offices, kiosks, and Orange service points that exists in every mall.
Currently the price for a SIM card charged with 40 NIS, costs 50 NIS (Israel post office price, other providers may have different prices.)
There is another cellular provider called Cellcom, and their prepaid card is called TalkMan. They don't state the date connection prices on their website, but I believe both Orange and Cellcom have similar prices.
You should know that it is very easy to find a free WiFi connection. You can find one in almost every restaurant, coffee, mall and most likely the hotel you will be staying in.
Read emails over WiFi connection. And additionally buy small data connection pack for emergencies.
Hope that was helpful. Enjoy your trip!
I think that MichaelS's answer, though complete when written, is a little out of date.
As of today, you can get a sim card from at least the following three providers at Israeli post offices:
If you are in some places with an Israeli "Home Center" store, you can buy a sim from "Home Cellular". The sim costs 29 shekels, and isn't charged with anything- after charging, it's 0.39 shekels for a minute/sms, and 0.5 shekels for a MB of data. I don't think these can be bought at the Post Office, but I could be wrong.
Also, Google Maps navigation does work now in Israel.
If your phone is unlocked' then instead of getting a Sim card from one of the main providers stated above (cellcom or orange) it is easier and cheaper to rent a sim card (you can get also a phone as well) for the short term period you need it for. You can get packages for data usage and cheap calls overseas. you can check the prices at http://www.israelphones.com . It also makes things alot easier...
Good luck, and enjoy your trip !