iPhone 3GS is using regular 3G upload which is hard capped at 384kbps. The download however is HSDPA which caps at 7.2mbps in theory.i don't think there is a "normal". my wife's i4 is seeing 3.5 down 2 up. my 3gs in the same location gets 2.5 down and .08 up.
It's normal to see lower download speeds on 3gs phone since your upload is choking the bandwidth, something similar we've been experiencing on iPhone 4 for the past month.