3.07 was the highest SW Level for the Dialog 4 that was ever built.
And you do not only need some Eproms with SW on it you also
need some hardware updates.
There where two different NSP versions the ones for the D4
(Standard for D4 NSP 55 256kB) and the ones normally used for C3 (NSP 56?)
The NSP56 was available at 128, 256, 512 and 1024 kB.
If your D4 has the NSP56 you can solder more memory to it.