How to tell if your roaming on the sprint iPhone 4?

Is the "o" the sign that tells you if your roaming?

The circle "O" means that you have no 3G or 4G buy still have service. Your phone will have no bars and say "searching" is when it's roaming.

Yes the "O" means you don't have service and in roaming, given that you have the iphone your plan is the everything data 450, the plan includes no roaming charges, so in case you roam there will be no additional cost but it is limited, for data roaming usage you have 300MB to use no charge if you exceed your service will be temporary interupted until you have coverage, and for calls while roaming within US territories no charge also, the minutes you spent on the phone will be deducted to your 450 minutes so watch out for your usage so you won't go over the minutes or it will charge you $0.45 per minute

You have Sprint which is a CDMA network.

If you are Roaming, it will say "Roaming" instead of "Sprint" for carrier. If it says "Extended", you are using Verizon or another partner's network. You only get roaming charges when it says "Roaming", and that only happens if you travel outside the USA.

Don't worry -- you won't get charged extra when it says "Extended".

Here's what all of the symbols mean…
"o" = slower data. It's basically the same as 2G but on Sprint's network.
"3G" = normal 3G data. This can be pretty fast, comparable to home broadband.
"LTE" = long term evolution. You have an iPhone 4, so you won't ever see this, but this data is EXTREMELY fast. Various tests on Cingular/AT&T and Verizon have shown 30Mbps or higher!

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For those that have a GSM iPhone (Cingular, T-Mobile, … ) here's what the symbols mean…
"o" = GPRS; 2G, same speed as regular dial-up (40-56kbps)
"E" = EDGE; 2G, decent performance
"3G" = 3G HSPA or UMTS, high-speed data
"4G" = HSPA+, which is considered 4G by AT&T and T-Mobile, really fast
"LTE" = long term evolution. Extremely fast. Virtually all carriers are adopting this for new phones