Hours after NASA leader Raila Odinga migrated from Safaricom to Airtel, Siaya residents thronged Airtel shops in the town.
They said they have made the decision following Raila's call to boycott Safaricom product, claiming the firm influenced the presidential election.
The telecommunications giant has denied claims it was involved in rigging.
"Now that we have seen our leader at the Airtel shop, that automatically means Airtel is now the better option and not Safaricom," Onyango Fred said on Monday.
Ogolla, another resident, said it would be wise for Safaricom to suspend its services in NASA strongholds as they will incur massive losses.
"I want to assure them that if our routine demonstrations kick off, not even Safaricom boosters and Mpesa kiosks will be spared," he said.
Airtel personnel were eager to assist the new customers and gave them gift bags with their purchases.
Raila officially migrated his Safaricom line to Airtel on Monday.
Supporters of the National Super Alliance are also to avoid products by Bidco and Brookside Dairy.
Last week, NASA legislators noted the boycott was part of the economic liberation scheme supported by the People's Assembly.
The move is among strategies the Opposition has employed in their national resistance movement. The goal is to bring the companies to their knees.
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Safaricom Dealers Association has urged NASA to call off its boycott saying 1 million Kenyans risk losing their jobs.
Chairperson Esther Muchemi said the political stalemate and campaigns for election has already lowered Mpesa commissions.
She said the boycott will force them to downsize in order to meet operational costs.
"This is purely bad politics. We urge our politicians to sober up. We are choking. Let them calm down and listen to us. Let them stick to politics and let us run the businesses," she said at a press briefing aired on KTN on Monday.
The dealers' association operates independently but has members authorised by Safaricom.