I have just gone through a lot of annoyance getting my Telus Milestone on Bell networks and figured I'd share what I've done to make this happen.
I had a Blackberry tour with Bell, but I didn't like it much and wanted to develop applications for Android, and I absolutely loved the look and feel of the Milestone, so I decided to either get it from Europe or here in Canada.
So, first off, Telus won't sell you the Milestone if you're not a customer of them - which means that if you want it with another carrier or for something else, you have to buy a SIM card to use with the phone - this will cost around 50 bucks, unless you buy it online where it should be free.
Even if you buy it without a contract for the full price, it is not unlocked (I don't get this country...) so you'll need to contact someone who can unlock it for you. Telus won't do it, but should be able to about one month after you bought the phone, or so I was told.
The phone unlocking service I used was Phone Unlock & Mobile Unlocking Codes - ThePhoneUnlockers.com - they were having some technical issues when I bought my unlock code, but I got it after re-verifying the information (they want the model number under the battery, not the model name as given by Motorola) and about 24 hours of waiting.
The phone unlocking is slightly confusing, as it uses the word "pin", when it is a phone subsidy code unlock.
If you turn on the Milestone with a non-Telus SIM-card then it will ask you for this code. I could only use a pure number code, and not the number-and-letters-codes I also received (they send more than one to make sure).
I messed around with this for some time because if you try to open this unlock code window by pressing star (alt + k on the slide out keyboard) it will start a default search instead. It takes some time to get into this code unlock window and I've had success with different methods: opening the settings and pressing * from there, having options in an application and then pressing *, and so on...
When you do get the code successfully typed in, it should unlock without problems - unless you're on Bell.
Since I had a Blackberry I had to change the SIM-card and data plan to something compatible, and the information regarding this is confusing at best. It is about 50/50 weather you talk to someone who understands this concept, bothers to or feels like going through it with you. My best experience was a Bell store - preferably someone senior who knows what they're doing. Phone tech support was useless and information often wrong or misgiving.
After I had a SIM-card that would work in the phone it should have been done and over with - but no, you need to set up the data settings for it to work properly, since the Milestone is not officially supported by Bell.
The information and help regarding this is also often wrong and misleading, so I finally worked it out myself by using the settings for new PDA/unlisted phones given on the Bell website.
I went to:
Settings-> Wireless & Networks -> Mobile Networks (select Bell here) -> Access Point Names.
Here, create a new APN (menu button and then New) and type in these bits of information:
Name: (Any name is good here I think, I put Bell)
That's it. After that I was able to connect properly, use 3G and everything seems to work fine now.
I've been struggling with this for days, so I hope this information can help someone in the same situation.