It was in Cambodian and since I do not speak the language, I could not tell what the message said. I called them back and they spoke to me in broken English and told me they had my number in their system and would take me out. I couldn't really understand what type of business they had but I have also received a few similar calls from another number with a 619- are code.

According to my Cambodian wife, this is a recorded message offering calling cards for sale.  If the person that they are calling is interested, then they are supposed to call them back at a telephone number they provide in the message (in Khmer, the language of Cambodia) to make the purchase.
   Whether the service is any good or not, I don't know.  You are supposed to pay for the calling cards with a credit card, and I'm not sure if I trust them.  Once my wife, who wants to give it a try, starts qualifying for credit cards on her own (she just got her Employment Authorization Document [EAD] a couple of months ago)then she can try them out on her own accord.

Exactly.. if you have ever purchased a calling card using your phone number, or someone called your number using a calling card to call Cambodia, that is how they have your number.. happened two days after I let someone use my cell phone and ever since. and since it is likely out of the US, theres nothing you can do to stop it.. they are using calling cards with US access numbers to call you..

There is more to these calls than we know.   I have received calls from
215, 562 and 209 area codes and they all seem the same.   I have blocked these calls and then they started blocking their number.   Nights, weekends.    Very frustrating.    I had two weeks free of these calls and they started again last night.