There is a new neat utility from sunbug - it can convert tavestates from PocketGBA to VisualBoyAdvance and vice-versa.

http://www.sunbug.net/products/emul/PocketGBA.html#convert

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PocketGBACon converts VisualBoyAdvance(VBA)'s save file into PocketGBA's save file. This program also convert PocketGBA's save file into VisualBoyAdvance(VBA)'s save file, but this converting is unstable.
VBA -> PocketGBA
Select VBA's save file(*.sgm)
PocketGBACon converts selected file into PocketGBA's save file(*.sv0)
Copy converted file to your PocketGBA 'SaveData' folder
Notes that '*.sv0' is a save file of SLOT#1.
PocketGBA -> VBA
Select PocketGBA's save file(*.sv0)
Select cartridge(ROM) file(*.gba)
PocketGBACon converts selected file into VBA's save file( *1.sgm )
Notes that this converting is unstable