I am a great fan of Prosecco and we always have a bottle at lunchtime when we're in Italy.
Prosecco is the name of a grape variety and its also the name used for a sparkling wine made all or primarily from the Prosecco grape.
There are two styles of sparkling, fully sparkling and frizzante which is less sparkling.
Prosecco fizz is not made by the champagne method, rather it is tank fermented under pressure.
Because anyone who makes a wine from Prosecco grapes can call their wine Prosecco even if it is still the serious makers of the fizz want to get some legal protection and in the finest area of Conegliano Valdobbiadene they enforce them for the DOC. Up to 15% of other varieties can be used in Conegliano Valdobbiadene DOC, but they are Verdiso, Perera and Bianchetta, not names I've come across.
I wentto a tasting organised by the Consorzio Conegliano Valdobbiadene and was very impressed by their wines & would suggest looking for the name on bottles of Prosecco.
Regarding a discussion between Pinot Grigio and Prosecco sparklers -- well there is little thatcan be said. They are different varieties and so will taste differently, but we don't know where the Pinot Grigio came from or how it got its fizz...
Have a look at
http://www.prosecco.it/