The cards were purchased from the Spotlight, a right-wing newspaper, and were renewed by someone using the name Daryl Bridges, according to William Sweet, the magazine's former marketing director.
Prosecutors say Bridges was one of the aliases Nichols used in his attempt to help McVeigh, the man executed for the blast that destroyed the Alfred P. Murrah Federal Building on April 19, 1995. The attack killed 168 people.
Sweet said letters containing renewal payments for the phone cards had a return address of Decker, Mich., which proved to be the home of Nichols' brother, James Nichols. The envelopes had upside-down American flag postage stamps, Sweet said.
Nichols also is accused of using the alias Mike Havens to buy 2,000 pounds of ammonium nitrate fertilizer a little more than six months before the bombing. The fertilizer was a key ingredient in the bomb.
Nichols is on trial on 161 state counts of murder. He is already serving a life sentence on federal charges for the deaths of eight federal law officers.
The state charges are for the 160 other victims and one victim's fetus. Prosecutors hope to send Nichols to the death chamber for his role in what was once the deadliest act of terrorism on U.S. soil.
The defense plans to argued that Nichols, who was home in Kansas when the bomb went off, was the fall guy for a shadowy group of conspirators, possibly including members of a white supremacist, anti-government group.