My partner has a Galaxy S I9000. The phone’s internal memory is getting low (around 1 gb left) while the internal SD card still has a lot of spare capacity (approx 5 gb left). Yet, when I try to move apps to SD card (via manage applications) the phone says it is unable to transfer due to insufficient memory? It also looks like the phone has facility to take an external SD card as well. I am hoping someone can explain to me:

 The relationship between the internal memory and SD card – why can’t I move apps? If I am not permitted to move apps manually, how does the phone choose how it allocates storage between the internal memory and internal SD card? Are there predetermined rules about what goes where? 

If I purchase an external SD card,  Will all my problems be solved? If I install an external SD card, will the move apps function in manage apps automatically default to the external card? If not, is there an easy way to transfer apps to the external card? 

Thanks in advance