Step (1) Verify That You Have the Right Phone and Data Plan
Using your BlackBerry smartphone as a tethered modem is a great way
to get connected to the Internet when you don't have access to another
network. But it requires the right equipment, and the right data plan.
Before you get started, you should check that your phone can be used as a tethered modem. BlackBerry's Website has a
list of supported phones.
If you don't see your phone on the list, check with your carrier to see if the functionality is supported.
And, before you do anything, you should check the details of your
phone's data plan. When using your BlackBerry as a tethered modem,
you'll be transferring lots of data, so you'll need an appropriate plan.
And remember, even if you have an unlimited data plan, it still may not
support tethered modem use. You may need a specialized plan from your
carrier. Check with your carrier to see if this is the case; it's better
to know ahead of time, so you don't get socked with a huge bill later
on.
Step (2)
Install the BlackBerry Desktop Manager Software

Now that you know you have the right phone and
the necessary data plan, you'll need to install BlackBerry's Desktop
Manager software on your PC. This software works with Windows 2000, XP,
and Vista computers only; Mac users will need a third-party solution.
The BlackBerry Desktop Manager software will be included on the CD
that came with your phone. If you don't have access to the CD, you can
download the application
from Research In Motion's Website.
Step (3) Disable IP Header Compression
Research In Motion does not list this as a required step, so your
BlackBerry may work fine as a tethered modem if you skip this one. But
if you're having problems, try disabling the IP Header Compression.
To do this, go to the Control Panel, and then the "Network and Sharing Center."
Click "Manage network connections" from the list of options on the left.
You'll see the BlackBerry Modem connection you just created; right click on it and select "Properties."
Click the "Networking" tab.
Select "Internet Protocol (TCP/IP)"
Click "Properties," and then "Advanced."
Make sure the box that says "Use IP header compression" is not checked.
Click all of the OK buttons to exit.
Step (4) Connect Your BlackBerry to Your Computer via USB
Connect your BlackBerry smartphone to your computer via USB, using
the cord that came with it. If this is the first time you've connected
the phone, you'll see drivers automatically installing.
You can verify that the phone is connected by looking at the bottom
left-hand corner of the BlackBerry Desktop Manager app. If a phone is
connected, you'll see the PIN number.
Step (5) Enter BlackBerry Dial-Up Number, User Name and Password
In order to establish your connection, you'll need a number to
connect to. If you're using a CDMA or EvDO BlackBerry phone (one that
runs on the Verizon Wireless or Sprint networks), the number should be
*777.
If you're using a GPRS, EDGE, or UMTS BlackBerry (one that runs on
the AT&T or T-Mobile networks), the number should be *99.
If these numbers don't work, check with your cellular carrier. They may be able to provide you with an alternate number.
You'll also need a user name and password from your cellular carrier. If you don't know it, call them and ask how to find it.
You'll also want to give this newly-created connection a name that
will allow you to identify it in the future, such as BlackBerry Modem.
Enter this name in the "Connection name" field at the bottom of the
page.
You can test the connection if you'd like. Whether or not you test it
now, make sure to save it so you'll have all of the information you
just entered.
Step (6) Verify That the Modem Drivers Are Installed
The BlackBerry Desktop Manager application should automatically
install the modem drivers you need, but you'll want to make sure. To do
so, go to your computer's Control Panel.
From there, select "Phone and Modem Options."
Under the "Modems" tab, you should see a new modem listed. It will be
called "Standard Modem" and will be on a port such as COM7 or COM11.
(You'll also see any other modems you may have on your computer.)
Note: These directions are specific to Windows Vista, so you may see
slightly different names used if you're on a Windows 2000 or XP machine.
Step (7) Add a New Internet Connection
Go to your computer's Control Panel. From there, select "Network and Sharing Center."
From the list on the left side, choose "Set up a connection or network."
Then select "Connect to the Internet."
You'll be asked, "Do you want to use a connection you already have?"
Select "No, create new connection."
You'll be asked "How Do You Want to Connect?"
Choose dial-up.
You'll be asked "Which Modem Do You Want to Use?"
Choose the standard modem that you created earlier.
Step (8)
Verify That the Modem is Functioning
Go to your computer's Control Panel. From there, select "Phone and Modem Options."
Click on the "Modems" tab and select the "Standard Modem" you just created.
Click "Properties."
Click "Diagnostics."
Click "Query modem."
You should get a response that identifies it as a BlackBerry modem.
Step (9)
Set Up an Internet APN
For this step, you'll need some information from your cellular
carrier. Specifically, you'll need an initialization command and a
carrier-specific APN setting.
Once you have that information, go to your computer's Control Panel. From there, select "Phone and Modem Options."
Click on the "Modems" tab and select the "Standard Modem" again.
Click "Properties."
Click "Change Settings."
When the "Properties" window, reappears, click the "Advanced" tab.
In the "Extra initialization commands" field, type:
+cgdcont=1,"IP","<
your Internet APN>"
Click OK and then OK again to exit.
Step (10)
Connect to the Internet
Your BlackBerry Modem connection should now be ready to use.
In order to connect to the Internet, you'll need to have your
BlackBerry smartphone connected to your PC, and the BlackBerry Desktop
Manager software running.
Click on the Windows icon on the bottom left-hand side of your computer (or the "Start" button) and select "Connect to."
You'll see a list of all available connections. Highlight your BlackBerry Modem, and click "Connect."
Now you're connected!