How should I handle having a phone in the States?

I need a phone while I am in the States this summer for my internship. I think I have two options: a VoIP number or a pre-paid cell phone plan.

With the VoIP number I can have an SF or Seattle number for basically $4/month. That will give me a number that forwards over the Internet to my computer. If I am not logged into Gizmo (my VoIP client) you will get my voice mail and I get an email with the voice mail in it as a sound file. I can then make outgoing calls from my computer for $0.01/minute to the US, #0.03/minute to Canada.

My other option is to get a pre-paid cell phone through T-Mobile. For $100 I get 1000 minutes that are good for a year.

Now the perk of the VoIP number is cost. $4/month is pretty cheap to have a number I am reachable at. Problem is convenience. If I have to have my computer one and connected to the Net that limits when and where I can make a phone call. And what about getting last minute directions? I will have to pull out my Canadian cell phone for that and be charged $0.50/minute International roaming.

With the pre-paid cell phone plan, I get a US number that I can use in my cell phone. That means I don't have to worry about having my Canadian cell phone and its roaming. The drawback is calling costs, although I can still use Gizmo for outgoing calls when I want to.

But the other big perk with the pre-paid service is that I get to keep a US phone number as long as I have minutes on my account. So with the year-long numbers I have a year to use 1000 minutes which should be fine since I go down to the States often enough that it is nice to still have a working phone. But the really cool thing is I can make the number I get for this probably my permanent cell phone number in the States if I move back after I graduate. So disseminating the number as my US cell phone number would make sense.

It sounds like the pre-paid idea works out the best unless someone can convince me otherwise.