posting invoices from non sap software to sap

hi,

Experts,

I have an interesting scenario, one of my client uses an software called handled computing software for the retail customers , whaterver invoices happanes at the retailers that goes to back office of handhold software divsion. at the end of the days those invoices needs to transfered from non sap (handheld software division) to sap tables. could you please throw some light on it. will be greatly apprecaited

Thanks