Jet. in Jepps I think you will find that there is no such definition as an "IFR aircraft".
In the USA you may give a taxi call in G to ATC when on an IFR flight plan but you are not considered IFR until you are given your IFR clearance.
Thats why you can climb in E in VMC before being given your IFR clearance--- yes just as we climb in G now waiting for our IFR clearance.
In Australia , to stop E working correctly it was decided that once an IFR flight planned aircraft gave a taxi call to ATC it was then considered to be IFR which meant it could not enter class E in VMC without a clearance unless it cancelled IFR.