Hi Jerdung
It would take me a long time to create an AT command validation test rig 
I was kind of hoping that sort of testing would be carried out by SW.
For interest the only reason I was trying at+cgdcont=? is that I didn’t understand why context 3 was erroring. Having at+cgdcont=? would have been useful as it turns out that there is a whole story behind the two contexts.
Some other random =? commands to the modem - note the at+wppp=? response
at+kusbpcomp=?
+CME ERROR: 4
at+ccid=?
+CCID: 0000000000000000000000000000000000000000000000000000000000000000000000000
OK
at=?
+CME ERROR: 4
at+cgreg=?
+CGREG: (0,1,2,4)
OK
at+WPPP=?
+WPPP: (0-2),(1-2)
OK