you have to take both phones into the sprint store and they have codes and stuff to put on your cell phones and it will carry over. but both screens need to be visible.
Update - In Mid April 2008.
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I emailed Sprint your question about when/if they will acquire the Curve. Below is their response: Thank you for contacting Sprint. Thank you for contacting...
Yes, Sprint offer the Blackberry Curve cell phone. It can be purchased on Sprint's website, other websites, or at a Sprint store. It might be cheaper to buy a used one from another website.
No. It is not available on Blackberry devices at this time. Sprint has just made it available for Windows Mobile devices. Hopefully soon they will create an app for us Blackberry users.