"Nobody can bring me home except Their Majesties' graciousness or the will of the people," Thaksin said in his phone call, made from Hong Kong.
"The jail term means I have to be on the run for 10 years, but I want to ask my fellow citizens if they really want me out of the country that long."
About 90,000 of Thaksin's supporters, clad in red shirts signalling their pro-government stance, gathered at Rajamangala sports stadium to hear his speech.
Thaksin went on to verbally attack the generals who overthrew him in a September 2006 military coup, to wild cheers from the crowd.
"They have abused the legal process to get rid of me. I was overwhelmingly elected prime minister twice yet I was overthrown in a military coup, and survived an attempted assassination," he said.
Thai prosecutors are urging London to extradite Thaksin, who won two landslide election victories, but was ousted in a 2006 coup on accusations of corruption and abuses of power.
Thailand's military and police were on alert for Saturday's rally amid fears that the event could spark clashes with anti-government protesters.
"About 1,000 crowd control police are deployed at the site and 2,000 more are on standby, ready for reinforcement if we see signs of trouble," Major General Amnuay Nimmano, Bangkok's deputy police chief, said.
Colonel Sansern Kaewkumnerd, the Thai army spokesman, said that the military would be on alert to back up police.
Jatuporn Prompan, an MP from the ruling People Power Party (PPP), said that about 100,000 people were expected to attend the rally, which was organised by the United Front for Democracy Against Dictatorship (UDD).
The phone call was Thaksin's first speech to his supporters since he was sentenced.
He remains hugely popular among much of Thailand's rural population, but many in the cities revile him, accusing him of corruption and nepotism.