Can you listen to received calls again on your iPhone?
How do you know if someone listen to your phone calls?
You do not. The technology is not detectable by the average person.
How do you reactivate your old iPhone 3gs if you upgrade from the iPhone 3gs to the iPhone 4 and then lose or get it stolen how would you reactivate your old iPhone so you can use it again?
Yes, the IPhone 4 is now available. It became available in February.
Has anyone received calls from 999-999-9999 or 000-000-0000?
999-999-9999 or 000-000-0000 are "spoofed" numbers, which means that whoever called you "tricked" your caller ID to display an incorrect phone number. Telemarketers do this so you cannot complain...
Why does your iPhone 3g drop calls?
Unfourtunately, you can't, you will have to reenter the data.