The three men were part of a quartet of Iraqi nationals on trial in Bellinzona, in the canton of Ticino, since the end of February, charged with trying to plant an IS cell in Switzerland and planning terrorist attacks.
On Friday three of the four were found guilty and given prison sentences of up to four years eight months, reported news agency ATS.
The prosecution had requested a jail term of seven and a half years for two of them, including for the supposed ringleader, a wheelchair-bound 29-year-old who had “abused Swiss welfare”, it was reported earlier in the trial.
The fourth was found innocent and will receive damages of 1,092 francs.
The case rested on the interpretations of the quartet's communications on the social network Facebook and messaging service Skype, said ATS.
For the prosecution, the words they used – including one deemed a code for a bomb – indicated that they were trying to bring people and materials to Switzerland to prepare an attack.
The defence denied that interpretation.
Asked why he used coded language in the online communications, the principal suspect said he felt he was under permanent surveillance by the US, ATS reported.
However the defendants' lawyers did concede that their clients had violated Swiss residency laws, said ATS.
A paraplegic, the ringleader arrived in Switzerland in 2012 and obtained asylum.
He is thought to have joined a terrorist organization in Iraq as early as 2004, the media said at the start of the trial.
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Hospitalized in Schaffhausen in the north east of the country before being moved to a centre for paraplegics in the canton of Aargau, he is said to have maintained close links with this organization and to have planned terrorist attacks.
Despite operations and rehabilitation, the Iraqi was active on social media platforms and posted videos supporting sharia law and terrorism, according to the prosecution.
The investigation and arrests were triggered by intelligence from the United States that an Islamic State cell planned an attack on Swiss soil.