>Naomi suggests preparing the formatted value in advance; in addition to that, you can also use the transform() function in the report expression itself ( I suspect this would be simpler). Just set the report expression to something like:
>
>

>transform(MyField, pcFormatExp)
>

>
Hilmar,

This seems to work fine.

lcNumber = '1235678790'
lcFormat = '999,999,999'
?TRANSFORM(m.lcnumber, m.lcformat)