Where are you staying? It's been a while since I've been inside the park, but my parents live about 45 minutes away. There is no EVDO coverage so you'll be getting dial up speeds with an aircard if you're getting coverage where you're staying.

Poor. The old faithful area you may get a signal, otherwise near the gates the last time I checked. Most of the park is extended network, which won't support data on regular phones, although 'should' on an aircard. so much of the park is wilderness that doesn't get much of a signal permeating it, try the main areas and you may get enough of a signal to upload, but it will be slow. Update the roaming list before you go.