How does iPhone 4 choose roaming carriers?

I think how it works is AT&T has contract with other carriers to provide the roaming agreements. It probably just depends on the area your in as to which network the phone will connect to.

Goes on strongest signal available.

Rock, paper, scissors.

I too roamed in Canada recently and was on Bell 80% of the time while in Toronto up through highway 400, 69, Sudbury, and on Manitoulin Island, but with constant shifts to Telus and Rogers at other times.

My previous phones (eg Blackberry) let me lock the phone to a particular carrier to eliminate the constant switching based on signal strength.

The issues with this:
- I'd lose SMS texts from people because the phone would switch networks too often!
- Bell's 3G network seems to have DNS problems. Like, sometimes it will crap out for 2+ minutes when surfing to new sites but is fine with previous sites that likely have the IP cached in the phone. I'd prefer to pin it to Rogers...

I have searched for a setting which would lock a roaming partner. I have been driving across Canada with my ATT iPhone 3GS. My phone is constantly switching from Rogers to Telus to Bell. Certain US 1-800 numbers do not work while roaming with Telus. Now that I am in BC my phone is most often roaming with Telus and I can't reach these numbers nor force the phone to a carrier who supports the 1-800 numbers. My wife's ATT Blackberry Bold is most often on Rogers & she often has 5 bars of signal when I have one with Telus. I am quite positive my iPhone is not just picking the strongest signal. Does anyone have any answers on locking a roaming partner?

I'm not very sure as I am not in the US but perhaps this may help.

Go Settings > Carrier

Tap on 'Automatic' to deselect it (checkmark should disappear). Give it a minute to pick up signals from cellular networks in the area then choose the one that you prefer. I guess it should stay locked on to it thereafter.

To manually select a cellular carrier while roaming internationally: Settings > Carrier > Manual > Select carrier you want to roam on.

Ensure the following is switched "On": "Enable 3G", "Cellular Data" and "Data Roaming".

Tip: Check with your carrier on current roaming packages and roaming rates before leaving.

Nationwide roaming coverage map for Rogers HSPA+/EDGE/GSM network: http://www.rogers.com/web/content/wireless_network

Rogers customers traveling (not international visitors): http://www.rogers.com/web/content/add-ons/travelwithyourphone

WARNING: For international visitors of Canada if you roam on either Telus or Bell do not turn off "Enable 3G" in your iPhone network settings. If you do you will lose signal due to the way their cellular network differs from Rogers. Telus and Bell do not support EDGE (2.5G) and as such you can only use 3G when in a 3G coverage area. The iPhone does not support Telus/Bell EVDO network. With Rogers when traveling outside a 3G coverage area the iPhone will drop back to EDGE without dropping the call. Keep in mind just as in the USA EDGE does not support transmission of voice and data at the same time.

The problem is the setting isn't there. At least with my iphone 4 (iOS 4.0.2), the "carrier" setting to toggle, whether automatic or manual, has been removed.

My main issue with this iphone 4 is that it cannot hold consistent signal with a single network while roaming. I owned an AT&T iphone 3G and it had no problems roaming. I travel to canada frequently, because I live in a border state. When I am in canada my old iphone 3G would either automatically switch to the equivalent ROGERS network and stay there OR sparingly I would have to manually select the ROGERS network. In either case, it would stay on that network consistently whether it had a good or bad signal. However, with my new iphone 4, it is constantly scanning for a network or hopping networks. It even desperately attempts to connect to the AT&T network while in canada (only 15mins away from the border). The preferred action, of course is for it to connect to the ROGERS network in canada for TWO reasons. (1) in canada it would have a stronger signal on ROGERS compared to AT&T and (2) incurring roaming charges isn't a issue because I have a "Nationwide plus Canada Plan" from AT&T.

I'm not sure whether this is particular to my iPhone 4 or all iPhone 4's. Also, does it have anything to do with the absence of the old setting? It seems as though something has changed on a software level. It can no longer lock on to one network. Instead it's network hopping. This is bad because sometimes I lose calls and get delayed texts that would've otherwise come in.

BJMSH wrote:
I'm not very sure as I am not in the US but perhaps this may help.

Go Settings > Carrier

Tap on 'Automatic' to deselect it (checkmark should disappear). Give it a minute to pick up signals from cellular networks in the area then choose the one that you prefer. I guess it should stay locked on to it thereafter.

There is no Carrier setting on my settings menu. I want to disable roaming completely as I live near the mexico border here in Arizona and every time I lose ATT coverage I get TERCEL and then ATT sends a text message about data roaming. That text message costs me and I don't want it. I have data roaming turned off but want to turn off roaming for voice and text as well. How do I do that?

You can call AT&T, and they can block roaming on your account.

Thanks. Would be nice if they would let me pick and chose when I need roaming and when I didn't by a setting on the phone.