Is the i850 a good choice?

My employer currently gives me a cell phone and plan. They thought they were doing us a service and got us all i920 smartphones and I hate it! It is big, heavy and bulky and I don't use any of the features on it. I want a smaller phone and although I want an i880, it is just too expensive. I am looking at I850's on ebay for about $75. Would my sim from my I920 work in the i850?

I also have the $5/month internet plan and was wondering if that will still work on the I850 if I swap out the sim with my current sim card.

Thanks for all of your help!

I don't think the SIM cards will swap. i920 is a smartphone, i850 is not