Prioritize wifi networks

Is there any way of creating a priority ranking for wifi networks? At home I have two networks available (one my private network, one an open hotspot). Occasionally my iPhone phone picks up and locks to the Openzone even though my private network is available. I want to maintain the Open-zone for when I am away from home, it is a pain to keep 'forgetting' that network when arriving home, then logging into it when heading out.

It should be pretty easy to assign a 'favorite' network that is connected to over and above all others when it is present?

The feature is available in OSX so figure shoudl be a part of iOS4?????