I would advise you to contact your local Opel dealer with regard to fitting a hands free kit. The main reason for this is that your vehicle is wired with what is known as multiplex wiring. With modern vehicles, fitting any after-market accessory such as alarms and in your case hands free kits, can result in problems occuring in the future which would not be covered by your vehicles warranty.
Retail outlets will tell you that they've never had problem's fitting kits to new cars, but believe me this is not the case. Most modern vehicles need to be told (programed) that an additional device has been fitted, which only a main dealer can do. Now you may get lucky, and I'm sure that some will read this and say that they have a new car with a kit fitted by a retail outlet and never had a problem, but these problems can hibernate and occur when you least expect it and in my experience you will be left in limbo between the retailer and the main dealer both blaming each other. It might be a few quid extra (sometimes not) but the dealers kit will buy you peace of mind.