The sprint airave is configurable to either allow all sprint customers to use it, or it can be configured to only allow specific phone numbers (configurable up to 3 unique sprint phone numbers). It should also be noted that the airave does not yet provide EVDO data access. If you have a weak EVDO signal from a tower, your device will always prefer that data connection over the 1xRTT that the airave can provide. The only true way to have data access over your handheld to the airave would be a complete absence of an EVDO signal.
This may not be much of a deal if you 1) don't use much data and 2) are in your own home with access to a PC.