How to get read-write access for your iPhone filesystem?

Use AppSnapp. It’s a web based script that installs Installer.app that shall enable you to catalog and install other third party applications on your iPhone. To download AppSnapp, visit WWW.JailBreakMe.com

Some Snippets:
It exploits a security flaw in iPhone, but also patches it after installation
AppSnapp was released last Sunday
Ever since, it has been downloaded 144,000 times on 100,000 devices
The development team works on donations (only $1500 so far).

Should I buy iPhones from Canada?

Get if from US, if possible.

Deal you get in Canada (December 7, 2007 onward)
Selling price                    $499 CAD ($520 USD)
Network                          Rogers Wireless for Three years

Deal you get in US
Selling price                    $399 USD
Nework                           AT&T for Two years

Why are iPhones locked?

Because of the profit Apple stands to make by maintaining the exclusivity of the deal with AT&T

Amount AT&T pays per iPhone connection in one month                            $18
Amount AT&T pays per iPhone connection in the two year period            $ 432

Money Apple possibly shall lose due to unlocked iPhones so far (250,000X432) : $108 million in the two year period

Is there a restriction on iPhone purchase?

Yes. Apple has recently announced this. Here on, you may only purchase iPhones on credit card (No cash). Also, you may purchase not more than two units. So, Why is Apple restricting the sales? Because, of the 1.4 million units of iPhones sold in the fourth quarter, 250000 were either resold or went to the unlockers for the phone to be unlocked. So Apple wants the iPhones to only go into the hands of genuine buyers.