Hi,
The user fields 1 & 2 in service tab of PO are free numeric fields where user can store additional information in numeric form. The user fields 3 & 4 are free text fields.
The values for these fields are accessible from ESLL table. You may use the same as selection / output of the custom reports.
As of my knowledge, these fields are not visible in standard reports.
Regards,
AKPT