Monthly earnings that trigger a trial work period

In 2009, any month in which earnings exceed $700 is considered a month of services for an individual's trial work period.

Social Security does not consider services performed during the trial work period as showing that the disability has ended until services have been performed in at least 9 months (not necessarily consecutive) in a rolling 60-month period.

See here for details :
http://www.ssa.gov/OACT/COLA/twp.html
http://www.ssa.gov/disabilityresearch/wi/detailedinfo.htm