iPhone GPS Abroad

Hi all,
I've got an app on my iPhone called 'Geotag Photos Pro' and I use it to geotag the photos I take with my DSLR. It works just perfectly in the UK (where I live) but I'm going on holiday to Egypt in 4 weeks and still want to use the app but don't want to incur any data charges by having my iPhone on.
I've tried using the App in airplane mode, but it wont then allow me to use GPS. What do I have to turn off on my iPhone to avoid a large phone bill?

Extra info:
I don't need an internet connection for the app to work.

Thanks

Roaming is only thing that cost you much in the phone bill.. close all the roaming apps.. and for the internet you have close all the internet apps or taking this step fast you can close the data roaming cause it workd in egypt ( I live there & I am answering you cause I was in the same situation likes yours but in the UK )

gd luck