Thanks, FidoJonathan. I suspect that not many users bother to change the memory card, which may mean that 2GB is plenty for most purposes. With so many seemingly different types available, it is comforting to think that virtually any micro will work should I want to go that route.
When I went to the Sony Ericsson site they specify a "Scandisk 16GB" microsd hc card as the maximum size. The Scandisk 16GB card is a class 4. I had a 16GB class 2 card in mine and had some issues but I can't prove that it was the problem. BTW, higher numbers for faster cards.
The Vivaz Pro can utilize microSDHC up to a maximum of 32GB according to both user manual and tech specs. Currently my brother has an Adata 16GB class 6 in his and has no issues with it.