Q: iphone 4s no signal

Off the top of my head I can think of at least a dozen reasons this might happen. So a little more information would be necessary, rather than me listing all of the possibilities. What country? What carrier? Do you have an account with the carrier? Is the phone jailbroken or hacked? Did it ever work? Have you contacted the carrier to see if they have a local service outage?

Just throwing this out there but this may help you:

If your iPhone 4s says you have no service, try using data or texting somebody. My 4s sometimes says I have no service with 3G but I'm still able to use data and send texts and make calls.

If you legitemately have no service, check that your SIM card is registered with your carrier and activated properly, and that your iPhone works with that carrier. Make sure you're not using your phone in the middle of a concrete or metal building, as this will greatly affect the service you will receive on your phone. Make sure you're not covering the antennae on the iPhone (the black lines on the metal band running around the sides of the iPhone are the antennae; the top two are CDMA and the bottom two are HSPA; you're using HSPA if you have a SIM card).