You asked if there was a cost difference - At least with Sprint, there is.
There are two types of Blackberry service:
BIS (Blackberry Internet Service) - included with Data Plan
BES (Blackberry Enterprise Service) - $30 additional on top of Data Plan
If you need to sync your Blackberry to the office for mail, calendar, etc., you must pay for the BES service (or purchase an application that emulates Windows Active Sync ~ $100). If you only need email, BIS will allow this, as long as your company is running Outlook Web Access (OWA).
If you are using Android, Palm, iPhone or smartphone, these will sync natively - including calendar, contacts, task lists, etc. - without the extra $30 per month (you still need the data plan). I have configured all of the above, including Blackberrys to sync with Exchange/Outlook. The Blackberry is the most complicated to configure.
Check with your IT department regarding phone policies first - just because a phone CAN sync, doesn't mean that it will be allowed to.
I recently renewed my contract with Sprint, and was able to replace two phones at a substantial discount. Initially I got a Blackberry Tour for myself, and a Palm Pixie (horrible phone!) for my wife. I had been using a Windows Smartphone (Motorola Q9C) that I had been quite happy with.
When I spoke with the Sales rep, I explained that we had a BES server, and I needed to make sure that the data plan would allow me to connect for no extra $. "Oh Yes!!!" I was told. After spending a few frustrating days trying to configure the phone and enlisting Sprint's useless help, I happened to Google upon the BES/BIS difference. Asking the right question to Sprint "Do I have the BIS, and not the BES plan?" revealed the answer - BIS. But for only $30 more I could upgrade to BES. Yeah-- right!
I decided to return the Pixie, give the Blackberry to my wife ( who did not need BES ) and ordered a Moment. I like my Moment - a lot! and do not regret not getting a Blackberry for myself. It syncs flawlessly to my office, and has many features and functions that I like a lot...BUT...
Battery life is still my biggest problem. I could live with the occasional CMDA lock-ups and other phone quicks - even Blackberry has it's quirks. There are those that say that they get 24-48 hours of use from their moment - I still get about 6-8 - even with doing all the techie things like flashing to the latest zefie custom kernal, and doing my own CL14 upgrade. I suspect its that I am just running too many apps and will be paring those down.
As far a a business phone - it depends. If you cannot charge your phone at least once or twice a day - I would stay away from the Moment. My Blackberry will go 2-3 days between charges.
In terms of email, calendar, contacts - both are very similar - except it will cost you $30 more a month for BES. You may also want to purchase DocsToGo for the android ($15-30). It is included on the blackberry. I personally prefer the calendar on the Moment.
In terms of applications, both have a lot to choose from. Blackberry seems to be more expensive on application prices, with far fewer excellent free apps.