hello,

how can I upgrade the memory of my sony ericsson p800 memory.

If you wanna upgrade dynamic memory, simply change your memory card, P800 use MemoryStick (MS). But if you wanna change rom memory, it's imposible

and sorry, I have to move your topic to SE box, this box for nokia only

is it like mmc where you just out in inside your phone, and how big can I get a memory stick.

No, it's smaller than MMC. The capacity is depend on your model phone, for example, P800 maybe support only 256mb