iPhone 3G No Service

Did you buy it new? If so, I would take it back and get another one if you can.

I would assume that these things can be tested for their RF sensitivity and transmission power at a competent repair center.

I did not buy it new im trying to recover from a bad buy on kijiji. Good suggestion, though i just googled four repair/service centers who all said "we dont do that here take it to apple they'll help". And apple is glad to tell me they cant touch the device as its out of warranty.

I'm sorry about your luck. I have that you really need to check what you want to buy from an auction house. If it's dirt cheap, then there's usually something wrong with it or it's stolen. That's why I only deal with companies that offer consumer's protection, especially with something like an iPhone. Keep looking around, there's somebody will fix it for you, though it might end up costing as much as a new phone.

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I had similar problem in iphone 3G I bought in Taiwan from Apple Shop and was using in India in 2G that time.

Basic problem was unless the signal was strong it was not working.But same Sim card in my Nokia phone was fine . Apple service center could not solve (they did not want to open since it was in Warranty ),I sent it back to Taiwan via my friend.The dealer replaced the phone.

It is working now.2G/3G/wifi.I think contact between SIM card and phone was weak

it most often reads no service unless im within a 3g network

So it does work when you have network coverage?

I'm having a hard time understanding the problem. An iPhone 3G should work when you are within range of a 3G network -- and that's what you say it does. It shows "no service" when you aren't within a 3G network.

What else are you expecting it to do that it is not doing?

Or is the issue that your phone is not picking up a signal when it should? That could be a device issue or a network issue. Several of my friends with iPhones have often complained about the lack of coverage for their devices. In that case, the phone is OK, it's just that there isn't a network available where they'd like one.

I think it is supposed to drop the 3G icon in the display, but still provide service if a non-3G service is available.

The big problem with these phones is that the indication of signal power is not quantitative. That is, it is not like a calibrated S-meter, just some ad-hoc set of bars that are supposed to make the customer happy.

However, a "No Service" message pretty much sums up that there is no network available or the phone's Rx/Tx ability is not up to par. Have a friend with the same phone stand by you and compare results.

Well, like you say: if there is no network, there is no service -- so what is the complaint?

The iPhone is a 3G device that will work on a GSM network or Wi-Fi. From what I can gather, there is no native application for VoIP on it for voice over WiFi, so you can do voice over a GSM network or data over GSM/GPRS/EDGE or data over WiFi.

Since the service provider furnishes the signal for both GSM and GSM/GPRS/EDGE, it is likely that you have both or none. (At least that's the way it would be in the USA.)

The number of bars is based on an RF measurement of signal quality and strength on the device and specifications provided to the manufacturer. For example, -95 dBm to -100 dBm, show 1 bar. Admittedly, the measuring capability in a mobile handset is not as good as a spectrum analyzer.

So, we go back to the question: is this a crappy device that is not picking up signal where it should, or is there no network available? If there is no network available, what is the device not doing that you expect it to do?

You wrote. "The number of bars is based on an RF measurement of signal quality and strength on the device and specifications provided to the manufacturer. For example, -95 dBm to -100 dBm, show 1 bar."

My understanding is that it is not calibrated to signal strength like an S-meter. In other words, the scale is not directly related to RF signal strength.

Notice that the iPhone's fifth bar represents a range of 40dB, whereas the fourth represents only 10dB.

Compounding the problem is that the signal strength is not as simple as RF signal strength. To make a connection requires both Rx and Tx reception. The signal is also digital, so multi-path errors, destructive interference, and other factors will cause signal degeneration in ways that an analog radio may not have an issue with.

We are saying the same thing, I think. Your example is just more comprehensive than mine.

Each phone has a method of determining signal strength (RSSI) and signal quality like SINR, SNR, or CINR. Each service provider provides specifications for handsets to manufacturers for the devices they intend to offer. Part of the specification is how many bars to show for what signal strength. Your chart reflects how that might look, or rather how it does look, for the iPhone. If the signal -- as measured at the device -- is between -51 dBm and -90 dBm, show 5 bars, if between -91 dBm and -100, show 4 bars, etc. Unlike an S-meter, this scale does not decrement in even steps. There are a couple of reasons for that.

First, as you point out, the signal is digital. The protocol used by the service provider (GSM, CDMA, iDEN or whatever) takes this into account and will employ several techniques to mitigate disruption. For example, individual frames may be repeated several times over the airlink. In technologies that use time-division, more time may be given to a particular user as the signal degrades. Some of these techniques may not come into play until the signal degrades to a certain point. In EVDO, as the signal degrades, more time slots are used and lower level modulation schemes are used. This slows the data throughput, but it allows the connection to stay active and for data to pass.

The second reason may be more about marketing than about technology. Each service provider wants their coverage to look as good as it can. So, the manufacturer is told what RSSI and/or signal quality to use to determine how many bars to show. Since we want to look good, we tell them to show 5 bars for the largest range. Note how the ranges become smaller as the number of bars decreases. This way, 5 bars will show more often than 1 bar.

So, in effect, what the bars are saying is "As long as you have 4 or 5 bars, everything ought to work OK and you'll be happy with our service. When you get down to one bar, things won't work as well."

I agree that the 'signal strength' bars are mainly a feel-good feature. My wife and I have different phones now, but back when they were the exact same model, operating under the same plan, we tried the side-by-side comparison when we hit low-reception zones. Her phone usually would work when mine wouldn't, but sometimes it went the other way round. We finally wrote it off to planetary alignment issues and the Jupiter Effect and quit worrying about it.

Part of the issue may have been that the cell phones were interfering with each other. When side by side, they are competing for the same resource -- a connection to the same tower. Both radios will transmit on the same frequency. Each cell phone will perceive the other one as interference. Depending on where the tower is and what other things are affecting the RF environment, one will have a better signal (more bars) than the other.

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I hate to say it, but this sure sounds like a sales pitch. My carrier also runs on the Sprint network for a whole lot less money and no loss in coverage even out in the middle of Nevada, "3bars" with no cell tower in sight

Yes you can get Lightyear for as low as 20.00 per mo. but you won't get all the options and if you refer customers to Sprint you won't get Free service. But if you refer customers to Lightyear you get FREE SERVICE!!! and if you got all the options from Sprint your bill would be $90 - $120 per mo. Plus you have to have a contract.

OP,

I might be going over covered ground here but you mentioned that the phone had been jail broken after getting little or no help with the initial problem. Google "3g no signal after jailbreak" and see if any of the hits that come up can offer some help. By jailbreaking the phone you might have compounded an existing problem.

I can only speak from my own experience, but when I'm out of my usual 3G coverage area the phone defaults to a local network and is still usable. Not knowing where you are or what the terrain is like, there may not actually be a local network to fall back on.

Just for grins, you might try downloading one of the free GPS apps and use it as a diagnostic tool, just to see if it works when the 'no service' message is shown.

There are also some diagnostic apps available that may give you a clue where your problem lies. However, I'd take any claims they make with a grain of salt. Read the reviews to get a somewhat useful feel for their actual utility.

How is the battery life? I've seen times when my battery charge seems to affect reception, especially in enclosed places. Maybe your battery just needs to be replaced.

Or, last resort, you could take the phone to a phone doctor and ask them to check the antenna connections and internal components. It's not impossible that the phone was exposed to a hostile environment (IE: dropped in water) at some point in time and is showing the results of internal damage.

Good luck!