In some countries using encryption is useless as they don't need to read your messages to think you're up to something. Merely using encryption is a signal for them to "intercept" you physically.
"Hide in plain sight" is a good phrase to google.

It does not matter whether you use wifi or gsm, the men in black sunglasses and hoods can track you anyway.
All it takes is a nice piece of SW on your device, it does not matter what kind of encryption you use brcause he interception can be done before the encryption, and same goes for location determining.

Now, if you are as badly concerned about this as you sound, you should worry that your device is already compromised when you unbox a new device fresh from shop. After all, you did not make the HW chips or compile the SW on it yourself so it is hopeless to make sure it's not compromised. After all, you cannot be sure that the device manufacturer has not been pressurised by government.

I've heard that wrapping tin foil around your head helps.

Yes, that is usually a good first measure.

The next step is to rip out all electric cabling that comes to your home, coz y never know what they will send thru the wires.

And water pipes too, see they put chemikalz in yr drinking water.

Maybe the OP can specify what exactly is the issue? Is the OP in some trouble hence asking for all this?

While I agree with most of the sentiment in this thread that attaining security and privacy in a mobile device is, to say the least, an uphill battle, let's not devolve into xenophobe mockery and state some facts, shall we? Paranoia begets curiosity, and curiosity begets knowledge

It all depends on your threat model. Commonly, one assumes that everyone is Out To Get You™. In this case, this implies that your carrier and the government cooperate. So this means that The Man knows about everything you send to or receive from your carrier. While you're logged into the mobile network, this includes approximate location data.

Even if your carrier doesn't cooperate fully, law enforcement can send a Silent SMS message to your device. This doesn't really do anything, but connection logs are generated at your carrier's facilities which can be requested on short order by the police.

Your device includes a GPS receiver. That in itself is not a risk. However, most producers of GPS chipsets (and thus, firmware) operate under the assumption that GPS radio data is always genuine and this means that it's automatically trusted. One simple attack is spoofing GPS satellites telling your receiver that it's equally far from all satellites it sees (which might be all that exist), in other words, that you're located in the center of Earth. Quite a few receivers hang, crash or overwrite their own memory when confronted with such input.

And of course, using GPS as a "secure" time source is ill-advised.

GSM is susceptible to man-in-the-middle attacks. Although the client authenticates against the network, the network doesn't authenticate against the client. UMTS fixes this. You need to force 3G in order to be secure against that. Even then, network certificates could be forged by a crafty attacker.

I'm pretty sure that tablet mode wasn't designed for any sort of security-sensitive scenario. Changing your IMEI would, in my limited view, only make sense if your current IMEI was somehow tainted or if it could be repeatedly rotated. Even then, your IMSI is fixed.

This just off the top of my head. If you insist on security, you'd do better with a laptop with Linux. In the extreme, the RMS approach.

Oh yeah, encrypted connections relying on certificate authorities aren't all that hot either, but I'm sure you knew that.

As juiceme has stated, device procurement is a headache even for big governments like the USofA's. At some point, you need to root your chain of trust somewhere.

Edit:

Did you hear about the NFC vulnerability paper? Yeah, the N9 is vulnerable, too. Because libpng in harmattan is old and vulnerable. Great, eh? This is an issue for all vectors where PNG images could come through. I.e., your browser. I don't think JPEG does much better. I'd even expect it to be worse.

And "Bluetooth security" is probably an oxy*****.

^ yep I got the shock of my life when my sister bluetooth'd into my phone and copied ALL MY FILES. It was a two way connection, but she had an older version of bluetooth (v1), so somehow she could access my files and I couldn't access hers. Creepy.

Also, explain the libpng thing. That just renders png images right? What's the security issue there?
Edit: Found it

One has to understand the risks and not use the mobile phone, or indeed any form of electronic communication, for anything sensitive. Simple as that.

BTW our own beloved forum has its own vulnerabilities too. Just look at how it censors not just whole words but also fragments.

tetris11_, harmattan ships with libpng 1.2.42. Until now, this library version has had five security-related bugs and more are uncovered all the time. All interpreters are susceptible to privilege escalating bugs to some degree. Generally, a specially crafted file could make the PNG (or JPEG, or GIF, or PDF, ...) library overwrite some of its own memory with some binary of the attacker's choosing.

There are countermeasures to this, none of them completely waterproof.

So, in principle, one could craft a PNG that, when displayed on an N9, would make it execute a piece of code with user privileges. The BlackHat paper outlines this.

no matter what you do if they want to track you they can . I could be wrong but maemo/meego should be more secure than android and iphone because they are a lot less in term of availaibility . As Dave said if they have the will and manpower they can do anything .