iPhone’s Problem 1

Last week, there was something wrong with my cell phone, iPhone 1st generation. I robbed this one from my wife one year ago. As we know, usually iPhone was sold with AT&T contract within US. This one is refurbished and sold without the contract. Most of time I am on campus, where there is wi-fi provided. It is not worthy spending extra money on data plan. During the past year, it worked very well for me. I do not have many calls every day, since I have a lot of contacts on my list. Several days ago, I called my friend, but there was no response when I pressed the numbers on the touchscreen. Then I tried to call them via VoIP, which transmit phone calls through wireless internet. The weired thing was that my friend could call me and I could pick up the phone. Google offered me a lot of help as usual. There are two choices that could solve the problem. One is resetting network settings, and the other is showing my caller ID. I tried both, but only the former works.