When the Digital Link wireless cellphone springboard was released last year, Sprint promised a 3G upgrade mid this year. No upgrade has arrived yet, and there will never be. According to Cnet, Sprint will offer a $250 credit towards any new Sprint PCS phone or data card for those who had bought the Sprint Digital Link thinking that it would be Vision upgradeable. This does not apply to anyone who received it from Handspring for free plus shipping and handling, as Handspring warned that it was not Vision compatible.
To get this credit you must contact a Sprint customer care person yourself, they will not contact you.
The reason that this is happening is that Sprint nor Airprime want to spend the money to create new software, and certify it for the Sprint network. With only about 1000 active Sprint Digital Link owners, it just is more cost effective.
The original VisorCentral.com review of the Digital Link may be found here