THE ONLY thing that changed was the nameplate. The pinstripes were the same, the bleach white background was the same and, yes, the number was the same. Yesterday, in front of a packed conference room at Citizens Bank Park, Roy Halladay smiled as he slipped on his new Phillies jersey, a virtual replica of the one Cliff Lee slipped off less than 2 months ago after the last of his four brilliant postseason starts.

Turns out, there wasn't enough room in town for two No. 34s.

"A baseball decision," was how general manager Ruben Amaro Jr. described the Phillies' rationale for trading Lee to the Mariners for pitching prospects Phillippe Aumont and Juan Ramirez and outfield prospect Tyson Gillies. And while that might sound like a cold way to describe the departure of a player who went 7-4 with a 3.39 ERA in 12 regular-season starts and turned in one of the most dominant postseason pitching performances in recent history, it also ensures that his departure will one day be subject to reckoning.

Financial decisions, which both Amaro and club president David Montgomery insisted this was not, are difficult to evaluate. Had the Phillies been operating under a hard $140 million payroll budget, prompting them to pave the way for the $9 million they would owe Halladay in 2010 by clearing Lee's $9 million figure from the books, there always would have existed some gray area.

Amaro said they had "internal discussions" about trading righthander Joe Blanton, who will be a free agent after this season, but decided that only Lee would attract the prospects necessary to offset the three players they sent to Toronto yesterday and the four they sent to Cleveland for Lee last summer. The decision, they said, was based on baseball, not on the fact that Lee earns $2 million more than Blanton is likely to earn through arbitration.

"If we had just acquired Roy and not moved Lee, we would have been in position to have lost seven of the best 10 prospects in our organization," Amaro said. "That is not the way you do business in baseball . . . There are a variety of reasons to make this move, but more than anything else this is a baseball decision."

Which leaves this: Either Aumont, Gillies and Ramirez will prove to be worth sacrificing 1 more year of Lee, or they won't. Like all baseball decisions, evaluating this one will take time.

The Phillies are very familiar with the Mariners. Phils assistant GM Benny Looper joined the Mariners as a scout in 1987 and spent the next 2 decades with the team, joining the Phillies last offseason after resigning as the M's vice president of player personnel. He was part of the decision-making team that signed all three players (Aumont as the 11th overall pick in 2007, Gillies out of the 25th round in 2006, and Ramirez out of Nicaragua in 2006). He is intimately familiar with their backgrounds: with Gillies' hearing impairment (which, according to Major League Baseball's official Web site, has left him with 30 percent hearing in one ear and 60 percent in the other), with the fact that Ramirez' mother was a volleyball player on the Nicaraguan national team.

The Phillies did not rely entirely on Looper's old notes. Their team of minor league scouts had the Mariners' system well-covered last season, Looper said.

Aumont is a 6-7, 220-pound righthander with a heavy 92-95 mph sinker who could be converted back to a starter (Aumont saved 16 games while posting a 3.88 ERA at high Class A High Desert and Double A West Tennessee). In describing Gillies, Looper used a lot of the words currently used to describe centerfielder Shane Victorino.

"High energy," he said. "All effort, all the time."

Gillies (6-2, 190) hit .341 with nine home runs and 44 stolen bases at High Desert. While Gillies wears hearing aids in both ears, Looper said it would not require anything more than a preliminary adjustment from his teammates in the field.

Ramirez is the rawest of the three - he went 8-10 with a 5.12 ERA in 28 appearances, 27 starts, at High Desert - but the Phillies like his upside.

All three will likely start the year at either Class A Clearwater or Double A Reading.

Lee, on the other hand, has already fulfilled his vast potential, winning a Cy Young in 2008 with the Indians before leading the Phillies down the stretch run last season. But with Lee 1 year away from free agency, the Phillies knew pairing him with Halladay would last just one season. And while such a pairing would have increased their odds of success this season, Amaro said he felt the best way to build long-term success was to sacrifice that one season for future prosperity.

Amaro said he had discussions with other clubs about Lee before deciding that Seattle could offer the best package. Both deals unfolded simultaneously because the Phillies wanted to make sure they could replenish their minor league system if they traded for Halladay.

"My job is to continue to have this club be a championship-caliber team not just for 2010, 2011 but for many years beyond that," Amaro said. "To that end, you have to have players in our system that will help us get there."

Lee already showed he could get them there. The rest remains to be seen.

For more Phillies coverage and opinion, read David Murphy's blog, High Cheese, at http://go.philly.com/highcheese.