The airline has introduced electronic upgrades that enable passengers with full-fare coach tickets to purchase upgrades to first or business class. Previously available in paper-coupon form in booklets of four, the 500-mile upgrades also enable Premier members to upgrade from most published fares. Four 500-mile upgrades cost $200; Premier members can purchase them for $125.As with the paper certificates, the airline will issue complimentary electronic upgrades to frequent fliers based on flight activity; Premier members receive four free upgrades after every 10,000 miles flown. Each 500-mile electronic upgrade will be valid for one year. If the upgrade goes unused, United automatically credits 500 miles to the passenger's frequent-flier account.

As is the case whenever any new system is implemented, there have been a few operational wrinkles. Eric Freidenrich, Premier Executive member from Woodside, Calif., describes United gate agents at having had "that deer in the headlights look" when he requested an electronic upgrade for a cross-country flight earlier this month. But by the time he made the trip home a week later, the agents appeared to be much more familiar with the process.

Mr. Freidenrich points out that the paperless upgrades mean that passengers no longer have to remember to pack their coupon booklets in their carry-ons, nor do they need to wait for mileage statements to be mailed in order to begin using any upgrades they may have earned.

But lucky fliers who have found themselves stretched out in first class because a gate agent forgot to ask for the upgrade certificate may find it harder to nab a "freebie" under the new system. The agent still has electronic access to the upgrade after the passenger has stepped out of the line. And while electronic upgrades are easy to view via United's Web site, some vigilance is required on the part of the passenger to keep track of the new paperless system.

"I check my e-balance after every flight just to make sure I've been charged correctly," Mr. Freidenrich says. "Before, they might not ask you for the certificate. Now, they can go ahead and ding your account without asking."