Former junior minister Ivor Callely has been jailed for five months for fraudulently claiming mobile expenses at Leinster House while he was a senator.

Callely, 56, of St Lawrence's Road in Clontarf, had pleaded guilty to four counts of using invoices believing them to be false instruments between November 2007 and December 2009 while he was a member of the Seanad.

Judge Mary Ellen Ring had adjourned sentencing to hear submissions on whether Callely's position as a former politician was an aggravating factor in the case.

She heard submissions from prosecution and defence on previous cases in Ireland, the UK and Canada, which related to cases involving a breach of trust.

This morning, through his barrister, Callely apologised to his former constituents.

Senior Counsel Michael O'Higgins said his client was remorseful and was very much aware he had let himself down.

He said he wanted to apologise to his Dublin constituents who he had represented for many years.  

Mr O'Higgins said custody should be a last port of call and not a first port of call.

He said Callely had put in bogus paperwork to support what would otherwise be valid claims and that the amount was at the lower end of the scale and had been repaid.   

During his trial, the court heard Callely used invoices from defunct businesses to claim phone expenses under an Oireachtas scheme that allows members to claim €750 every 18 months.

After he became aware of the scheme in August 2007, shortly after being appointed a senator, Callely began submitting for expenses at 18-month intervals.

He also submitted retrospective invoices from his time as a TD.

He fraudulently claimed a total of €4,207.45 using six invoices.

Judge Ring said a custodial sentence was required in the public interest.

Politicians were not expected to be superhuman, she said, and were allowed to get it wrong.

However, they were not expected to cut corners or rely on "entitlement" to explain misbehaviour or criminal actions.

She sentenced Callely to five months in prison, from today.

Callely, who was a member of Fianna Fáil, served as Minister of State in the health and transport departments between 2002 and 2005 and was later appointed to the Seanad where he remained until 2011.