You can use your phone (as long as you're not on prepaid) but I recommend adding the 3 day roaming packages on the day you leave. I also recommend you not use data roaming. It's really expensive so stick to wifi when it's available.
If you choose not to Add a roaming pack your rates are
.60 cents per text sent and received
1.50 Per Minute Voice
5$ Per MB Data
Here's a breakdown of the packages to add to your account.
You'll find them under Monthly Add-On's
3-Day U.S. Roaming Unlimited Text $10/month
For $10, enjoy unlimited text messaging while travelling within continental U.S., Hawaii and Alaska for 3 days.
To immediately add to your account, text 3TEXT to 4545.
Restrictions: Add-on does not auto-renew after 3 days. Includes international text messages while travelling within the U.S. Availability of service to international destinations will vary by country and is subject to change without notice. Excludes MMS messages (picture& video), premium messages and subscription based messages.
3-Day US Roaming Talk $10/month
For $10, get up to 25 U.S minutes of airtime while travelling within continental U.S., Hawaii and Alaska for 3 days. Minutes used while in the U.S. are charged separately from your regular monthly plan minutes
To immediately add to your account, text 3TALK to 4545.
Restrictions: Add-on does not auto-renew after 3 days. Includes calls within the U.S. and to Canada. U.S overage roaming rate of 45¢/min applies after the 25 included U.S. anytime minutes are used up. The airtime required to connect your calls is drawn from the included minutes. Excludes directory assistance calls (411) calls.
Alternatively you can unlock your phone and get a prepaid sim from An AT&T store and pay a few dollars a day for unlimited use.
If you've been a customer for 3 months with all of your bills paid on time Koodo will give you the unlock code for 50$.
You can unlock the phone through eBay or other sites like gsmliberty.com but doing so may void your warranty (although it's not usually something a carrier will look at when processing the warranty claim ) Source: http://help.koodomobile.com/getting-s...
If you are on prepaid your only option is to Unlock your phone and grab a USA Sim-Card. Koodo phones are mostly compatiable with AT&T's network. Not so much with T-Mobile (except the Galaxy s2x). And AT&T offers Pay per day use at a really great rate. Unlimited domestic use at 2$ per day. Source: http://www.att.com/shop/wireless/plan...