So far, this is what we know:

Model No: MC676LL/A iPhone 4 16GB (black)
Model No: MC678LL/A iPhone 4 32GB (black)

Available plans:
Talk: 450 min/mo ($.45 ea over) $39.99/mo
Talk: 900 min/mo w/unlimited to 5 selected people (any network) ($.40 ea over) $59.99/mo
Talk: Unlimited $69.99/mo

Data: Unlimited iPhone $29.99/mo
Data: Unlimited iPhone + 2GB tethering and Hotspot 3G ($20/GB over) $49.99/mo

Messaging: Pay-per-use $.20/text $.25/video/pic
Messaging: 250 messages/mo ($.10 ea over) $5/mo
Messaging: 500 messages/mo ($.10 ea over) $10/mo
Messaging: Unlimited $20/mo

Here are links:16GB32GB

Thanks, Joe!