[dmishe]

There are no roaming charges inside of US, are there?

[ghaff]

There can be roaming charges and roaming data caps inside the US although they're not very common with the major carriers. The only time I've specifically encountered a cap with AT&T (I have a grandfathered "unlimited" plan) was when I was in Furnace Creek in Death Valley. (For those not familiar, Furnace Creek is quite isolated but it did get cell phone service a few years back.)

As others have said, international roaming is very expensive without a specific plan. I left early on a trip to Europe last winter because of a snowstorm and before I knew it I had a big bill because I had used my phone in Toronto airport and my roaming service wasn't scheduled to begin for a couple of days. Fortunately, AT&T moved the start time for the international service earlier for me.

[Steko]

AFAIK AT&T always lets you buy International plan add ons back to beginning of the current bill cycle. Still a rip.

T-Mobile has 'free international data' but it's 2G speeds (capped at 128 kbps) and the upsell is a rip, $50 for half a GB.

[Maultasche]

There are no rules against roaming charges, so it depends on the plan.

I believe that most plans don't have roaming charges within the United States. Mine certainly doesn't. It's hard to have a competitive plan that has roaming charges.

Roaming charges outside the United States can be quite high. I have to watch carefully who I'm connected to when I'm near the Canadian border.

[aeorgnoieang]

There are; outside of each carrier's coverage. Tho some carriers don't have roaming charges.