Just watched T2 and when he is at Dyson's place it is his walkie talkie that he hears the trouble at Cyberdyne? Also he has his sub machine gun before he crashes his bike into the helicopter, then he morphs through the hole and he uses the same gun to shoot at the swat van.
Perhaps that walkie talkie was another real working one from the biker cop. And the SMG, if indeed he is seen with it before the helicopter morph, perhaps he ermm...internalised it and brought it into the helicopter that way.