3G Broadband Card vs. Tethering

If you use a smartphone, do you also carry a separate 3G broadband card for your mobile computer? Why not tether using your smartphone?

My Lenovo ThinkPad has a built-in 3G radio, but I would need to use AT&T if I wanted to use the internal wireless card. I could also get a 3G mobile broadband USB card for any of the major wireless providers in my area. Does it make sense to get a separate card if I can also tether?

The only reason it doesn't make sense is money. If you're trying to save money, then tether.

Otherwise, here are several reasons why you should consider a dedicated 3G wireless card for your mobile computer:

1. Save battery life on your smartphone. (smartphones can have trouble charging if you're connecting via a USB cable to tether)
2. Talk and surf. If you're tethering, you can't talk and surf simultaneously. So, if you need Internet access while you're talking on the phone, you'll need a separate connection.
3. Reliable connection. Tethering is reliable, but not as reliable as a dedicated broadband card. 
4. Heat. Tethering will probably heat up your smartphone. That can also lead to a shorter battery life span.
5. Sharing. Do you ever need to share that 3G broadband wireless card? It's much more difficult to share your smartphone.
6. Bulk. Why have anything connected to your mobile device if your computer has an internal built-in radio? 

I realize that dedicated 3G wireless plans are expensive. We're talking about roughly $60/month just for the data access. When 4G networks roll out, that price could even go up. Or, you may need to choose among different data plans for your dedicated broadband access card.