US Mobile Carriers and What Their IP Addresses Look Like

The United States has three nationwide mobile carriers that issue their own SIMs and run their own radio networks: AT&T, T-Mobile and Verizon. Every mobile proxy in the country ultimately exits on an address owned by one of them, or by a smaller operator that rides on their networks. This page describes what those addresses look like to a website, an IP lookup service or a fraud-scoring tool: which autonomous systems announce them, how carrier-grade NAT shares them, where geolocation places them, and how the three carriers differ in practice. Mobile Proxy USA runs SIMs from all three in its eight US metros, and the facts below apply equally to each.

Who owns the address: autonomous systems

Every public IP address is announced to the internet by an autonomous system, identified by an AS number. The AS number is the most reliable way to tell which carrier an address belongs to, because it comes from routing data rather than from a guess. AT&T Mobility announces its subscriber ranges under AS20057. T-Mobile USA announces under AS21928. Verizon Wireless announces under AS22394, and some older Verizon ranges still appear under AS6167, the number inherited from Cellco Partnership.

An IP lookup on a Mobile Proxy USA line therefore shows one of those AS numbers together with the carrier's name as the organisation. Reputation services such as IPQualityScore, Scamalytics and MaxMind read the same data and tag the address with a connection type of cellular or mobile. That tag, more than the specific number, is what distinguishes a mobile proxy from a residential or datacenter one.

One address, many phones: CGNAT

US carriers do not have enough public IPv4 addresses to give one to every subscriber, so they use carrier-grade network address translation. Each phone receives a private address inside the carrier network, and a translation gateway maps many such phones onto one public address when their traffic leaves for the internet. The number of devices behind a single public address varies by carrier and gateway, but it is routinely in the hundreds or thousands.

For a website this means an AT&T or Verizon address is never one person. Blocking it, or treating it as suspicious because of past activity, would affect every subscriber behind it. Sites therefore judge carrier traffic mostly by behaviour: request rate, session consistency, browser signals. For a proxy user this is the main advantage of a mobile address over a datacenter address, where one IP really does mean one machine.

The same mechanism explains two things buyers notice. First, a rotated address can repeat: the carrier gateway has a finite pool and hands out whatever is free. Second, a fraud-score tool may show a non-zero score on a fresh address, because someone else behind the same public IP did something earlier in the day. Neither is caused by the proxy.

Where the address geolocates

Geolocation databases place a carrier address at the location of the translation gateway, or at the location the carrier registers for that block, not at the position of the phone. The three carriers behave differently. T-Mobile addresses tend to resolve to the metro the modem is in, or a nearby city in the same state. AT&T addresses resolve to a regional hub: Boston AT&T lines resolve to New York, for example, because the New England traffic leaves through the New York gateway. Verizon addresses can resolve a few hundred miles from the modem, and a Verizon line in one city may show a different city in the same region for a period before databases catch up.

State-level accuracy is good on all three, and country-level accuracy is effectively perfect. Buyers who need a specific city should prefer T-Mobile or AT&T in that city and verify with a lookup before relying on it. Buyers who only need a state or the country can use any carrier.

IPv4, IPv6 and what sites see

All three carriers run IPv6 internally and T-Mobile's network is IPv6-only on the phone side, with IPv4 provided by translation. A proxy connection to a site that supports IPv6 may therefore leave on an IPv6 address that is unique to the device, while a connection to an IPv4-only site leaves on the shared IPv4 address. Mobile Proxy USA lines are reached over IPv4 and exit on IPv4 by default, which is what most buyers want because the shared address carries the crowd effect described above.

Practical differences between the three carriers

AT&T has the widest geographic coverage and conservative gateway placement, so its addresses are stable and well-trusted but resolve to regional hubs. T-Mobile has the largest 5G footprint and the most metro-accurate geolocation, and its addresses change readily on reconnection. Verizon has strong coverage and high reputation scores, with the least precise city geolocation and, on some gateways, a tendency to hand back the same public address after a reconnection for a while.

On a Mobile Proxy USA line the carrier is selected at checkout and the city is selected with it. A line can be moved to another city at no cost with the remaining time carried over, which is the simplest way to test which carrier and gateway suits a particular job.

Frequently asked