Any scope would do really, you can for something like the entry level scope: http://www.picotech.com/picoscope2200-s ... tions.html
Then use x10 probes, what you may have to do is use the scope on a laptop without the power supply so that is floating to stop the ground of the PC interfering with the telephone lines.
Alternatively you can use a differential probe with the scope and that way you would not have to worry about grounding issues: http://accessories.picotech.com/active- ... robes.html
Or you can buy a differential scope: http://www.picotech.com/differential-oscilloscopes.html
Hope this helps.