You can simply install an emulator on an Android (or iOS, a little more difficult) smartphone. You can then play all the classics. (Allowed in Switzerland but "grey area").

Ok i thought maybe the 3ds has a gba slot like the older ds....

Yes I already had a gba emulator but then uninstalled it in favour of my real gba. The feeling is just not the same ;)

No schansse are too old and different format unfortunately.