I think that in Croatia exist this kind of numbers but calls from Serbia to the Croatia are not cheap. The best way should be to tell her to install one of the Betamax clients (FreeCall, VoipWise, lowratevoip, ecc). With these programs she can make call-back (her phone rings first, then rings your). Of course, you should charge this account.
:: Nemoj se svadjati sa budalom, ljudi cesto nece primjetiti razliku ::