What additional cost may occur from making my iphone a personal hotspot?

I turned on the personal hotspot option in settings on my iphone but it says additional costs may occur. Does that mean it costs money for me to connect my other devices or just if i exceed the amount of 3g i'm paying for.

If you turn hotspot on, you are charged for any data anyone uses though it, if your on a contract then as long as you don't go over its fine.

It might depend on the carrier, but as far as I know the only cost they're talking about is the charges you're going to incur from any data traffic that goes through that hotspot. If it's a huge amount of data it may exceed your data plan and you'll be charged for the excess.

But ATT for example doesn't charge you anything extra just to turn the hotspot on. At least for now. God knows they love to turn this kind of thing into a "special feature" and charge you some godawful fee just to use it, like they did with tethering. But for now the hotspot thing is just a feature on the phone with them.

It just means if you go past your data allowance it will start to charge you for the extra used, I've got unlimited data on my 4S so I don't have to worry! What network are you with? I'm with 3, they're the only network that has a brilliant connection!

There's a charge for using the feature at all.

For ATT you need to move to the $50 for 5GB + Mobile HotSpot Plan.
For VZ it is $20 + Your current data plan.
I do not know Sprints price.

(These all apply to relatively newer plans, any plan over 5 years old before this feature become popular may not require extra payment.)

Once you go over your allotted data then Att or VZ will start charging you overages on a per GB basis (usually they round to the nearest GB = $10-15/ GB)

Any extra costs depends on the carrier and the amount of data you signed up for. Assuming you are on a contract with one of the three carriers that sell iPhones, here is what you may have to pay:

On Verizon:

Unless you have a grandfathered unlimited data plan, you will have to pay $20/month for the mobile hotspot feature, in addition to how much ever you pay monthly for your data, and then you may have to pay for overage charges if you go over your allotted data for the month.

If you have one of their "Share Everything" plans, then the feature is free, but you an only use as much data as you have signed up for without paying overage charges.

On AT&T:

You have to either have a 5 GB data plan ($50/month), which includes the mobile hotspot feature for up to 5 GB, or a grandfathered unlimited data plan.

On Sprint:

Sprint offers unlimited data, but you have to pay $20/month for the hotspot feature.