Sprint's official data policy about tethering does not allow using the phone as a modem without a specific plan:
Promotions, Options and Other Provisions Data...Except with Phone-as-Modem plans, you may not use a phone (including a Bluetooth phone) as a modem in connection with a computer, PDA, or similar device. General Terms and Conditions of Service Specific Terms & Restrictions On Using Data Services In addition to the rules for using all of our other Services, unless we identify the Service or Device that you have selected as specifically intended for that purpose... If your Services include web or data access, you also can't use your Device as a modem for computers or other equipment, unless we identify the Service or Device you have selected as specifically intended for that purpose (for example, with "phone as modem" plans, Sprint Mobile Broadband card plans, wireless router plans, etc.).
Sprint had a Phone as a Modem (PAM) data option back in 2008. Customers who still have this add-on are "grandfathered" and may still have the tethering option.
How To Go Online With Your Laptop Using Sprint PCS
Therefore, to access the Internet on your laptop over Sprint's network, you'll need to get a separate mobile broadband service plan for your laptop and either a mobile broadband network card or a portable mobile hotspot device.
Sprint's 4G Mobile Broadband service may be worth the extra equipment and service charge for mobile professionals who need faster-than-3G speeds. Sprint's Simply Everything + Mobile Boradband plan is, at the time of this writing, $149.99 per month.
The Mobile Hotspot add-on plan is $29.99 per month and capped at 5GB but you can add it on per day for $1 per day.