What does this mean? Imessage

When I try to send a message to a new number (my friend) it changes from message to imessage meaning they have an iphone. So when I actually send a message it doesn't show delivered or anything, then I waited like 5 minutes and it finally converted to text message. I tried calling their number but it says the number you're trying to reach is unavailable. But then I try to send them a message again (since I don't have them in my contacts) and it goes from regular message to imessage again. Does this mean they have imessage but no phone line or what? Technically my messages aren't getting sent either, right?

A Good Program To Browse My iPhone's Filesystem?

I used to have a program called iPhone Browser, and it worked pretty well. But now it stopped working. So I just would like a program to allow me to browse my entire filesystem on my iPhone 4S, without getting any viruses.

Any suggestions?

How to know which iphone is it?

I got a iphone from. My uncle without its box and all

it was just the phone… I don't know which one is it? 4 4s or 5
how woud i knw it?
can't ask my uncle as he left for usa and i'm in india

Iphone keeps shutting off? Why?

This has happened 3 times now. My iphone 4s which I have had for 7months, I brought as a grade a refurbished iphone from a sale shop online. It came with a 12month warranty. It has suddenly crashed then the apple logo will appear and then it will go and then it will appear again. It does this repeatedly. The screen remains illuminated. I have left my phone to go completely flat before I have plugged it in to charge it and it has been okay again. I have also had several apps including my messages crashing and not allowing me to use them until i turn off the device and back on again. It has also a few time crashed but turned back on again without problems.
Why is this and how should I fix it?
Do you think I should contact the store I purchased it from to get it repaired or replaced under the warranty?