When Novatel Wireless released the Merlin XU870, an ExpressCard/32 3G mobile broadband device, they included instructions on how to use it on a Mac OS X machine. And while I was able to successfully connect to my wireless carrier with the product it suffered from a number of limitations:

• The card was not recognized if it was already in my MacBook Pro when it was turned on. To use the device at all it had to be inserted after OS X was fully booted
• About 75% of the time it would not disconnect from my carrier after I had established a connection. I would get a "Disconnecting..." message forever. There didn't seem to be any way of forcing a disconnect, and it never timed out. Popping out the XU870 would result in a warning message about lost data.
• It seemed to make my trackpad go all wonky. I can't explain this other than to say that after I established a connection the trackpad in my MacBook Pro behaved erratically. Both devices are USB.

Despite all of this, I was happy with the performance of the device and felt it was a much better solution than connecting via bluetooth to a cell phone and using that as a modem.

Recently however Apple has released support for this (and other 3G devices). This update solves all of the problems I have listed above, but would not allow me to connect to my non-Cingular carrier (I use Fido in Canada). After trying many combinations of account details I dug into the supplied "WWAN Support" modem script supplied with the update. What I found was the APN for Cingular had been hard-coded.

To alter this for your carrier simply go to your primary hard disk in the /Library/Modem Scripts directory and look for the file called "WWAN Support". I made a copy of this and placed it on my desktop in case I messed it up. Drag this script to your favourite editor (I use TextWrangler) and scroll down to the bottom. You should see something like the following:

@LABEL 109
!Set the APN
write "AT+CGDCONT=1,\34IP\34,\34ISP.CINGULAR\34\13"
flush
matchclr
jump 6

You need to change the text "ISP.CINGULAR" in this file (don't touch any of the other characters) to whatever your carrier told you your APN was. For Fido it is "INTERNET.FIDO.CA". Thus, for me this line now looks like the following:

write "AT+CGDCONT=1,\34IP\34,\34INTERNET.FIDO.CA\34\13"

Write this back out.

You will also need to change your username and password in your networking preferences. Open "System Preferences" and click on the "Network" icon. Click on "Novatel Wireless HSDPA Modem" and then "Configure". For Fido my settings are:

• Service Provider: Fido
• Account Name: fido
• Password: fido
• Telephone Number: *99#

Note that the telephone number is NOT "internet.fido.ca" as it would be in other situations - this is the APN and is now hard-coded into your modem script. All other settings can be simply left at the defaults. Click "Apply Now" and then you can try it out.