wireless notification

I have been asked to look into creating a water sensor alarm and then to send when an alarm is present.

I know I can sense water and create a local alarm.

however, the building will be in the center of a city and I do not have any wired phone or wired internet.

my choices would to tag onto some open wifi, if there is one
or use a cell phone that is pre-paid and just waits for a problem.

since I do not have wired phone or internet, I am looking for suggestions to send out an alarm signal.

This product from Sparkfun may help. Just add a pre-paid SIM card and you can send SMS messages over the cellular network.

How far away from the alarm do you want to receive it? If it's only 500m (1/4 mile) then a radio solution like XBee/RFM22/Nordic will avoid the cost of the SIM card.