Making Laser Tripwire with Phone Messaging
As with any project, where you don't know where to start or what to use, there are a number of steps you should go through.

First define exactly how you want your system to work.  There are many many different ways of achieving what you talk about in your question, and most (if not all) of them can be performed using an Arduino of some form with extra hardware to do specific jobs.

Only when you have defined such things as:


What distance must your trip wire be effective over
How long will it be interrupted for typically
Will it be a permanent installation or a mobile battery operated system
What kind of messaging do you want on the phone
Must the message be receivable anywhere on the planet or just within a certain range of the tripwire system


For instance, for the communication, would you want to send a text message via the mobile phone network (SMS), or an email through the internet, or connect to a custom app using Bluetooth, etc., - there are a myriad of different possibilities.

Once you know exactly what you want it's then time to break the project down into little blocks.  Each block can then be tackled separately and you can research what is available to help you perform that specific task within the bounds of what you have specified in your requirements list.

Each of the blocks of your project are quite simple to create and there are generally examples and tutorials for most things on the web that can help you.