You can change any bell cdma phone to an unlocked hspa phone yourself. You just need a SIM card, and you use the Bell self care website, manage features, change my phone. You input the IMEI and the SIM card numbers, decide whether or not to keep the same plan, and your number will be switched to the new SIM. The only charge is for the SIM ($5 at a Bell store, also sold other various places for $10). There is no activation charge if you do it online. I have done this with three numbers, no trouble any time. In fact, you can then use the SIM card in any compatible hspa phone without further changes/activation.
The problem with a pre/pixi is that the bell network settings are not baked into WebOS, so unless the phone has been "palm activated" (not just bell activated), you can only get by the first use screen using the metadoctor, or palm's developer tool. Once by the first use screen, you need to get a copy of the CarrierNetworkSettings.db3 file and edit the network settings (there are various posts in the forums for doing this), so that you get data on bell. Rogers (and maybe Telus) setings are already there, so not a problem for Rogers.
The Pre 2 network settings are handled differently, and I don't know if bell is in there from the start. If not, it isn't clear how or what file to edit, as there is no CarrierNetworkSettings.db3 file in the extracted doctor for WebOS 2. Also, is a WebOS 2 metadoctor available?
So, you really don't need to go to a bell store at all, as long as you can get by the first use app and edit the network settings. Also, I don't think that bell will be much help with all of that. It is not their phone and they won't have any idea how to support it or do any of this.
The beauty of doing it this way is that when it is not their phone, their network can't identify it by the IMEI number, and for all they know it as a flip phone. You can put a minimal data plan on it (say mobile browser 50) and carry on. Their phone and they will insist you put a smartphone plan on it. I have an AT&T pre plus, pixi plus, and google nexus one all set up this way, no problems, and I move the SIM cards between them, again no problem.
As an aside, I also have mobile hotspot installed on the pre plus and the pixi plus, working well.
Also, bell does not track data properly on my hspa phones, each session capped at 0.0977 MB, total monthly usage on the bill usually 6-10 MB, but is about 400-700 MB tracked using netstat.
So, the three questions for Pre 2 are metadoctor availability, bell network settings baked in, and how to edit network settings when they are not there by default.