do you mean you are concerned that when you call her from out of hong kong that she will incur overseas call charges? this is what i understood from your post. if this is it, then don't worry, she will not. she will only have to pay for airtime, which is the same if you were in the same town calling her on her mobile.
ofcourse when calling you if she uses a calling card on her moblie, then she will not incur othe high overseas calling charges the mobile compnay charges but i believe she will still be charged the airtime.
so no way to avoid airtime charge (which isn't too bad here) but unless i misunderstood my salesperson, receiving an overseas call doesn't penalize me with overseas call charges (just standard air time).