• eSIMS are a way to purchase and provisions internet¹⁾ services quickly over the internet.²⁾
• this can be an easy way to get internet access where your main carrier lacks service
• traditional eSIMS are stored on a chip in your phone or other device
• physical eSIMSs are stored on a SIM card
• eSIM profiles (definitions) are downloaded from the provider to one of the locations above

about these summaries

Short-term usage: you have AT&T but will be camping where there is no AT&T signal. Your neighbors are getting good service from T-Mobile, so you buy a 7-day data eSIM plan for $5.20 that uses T-Mobile³⁾ and download it to your phone. Now you have T-Mobile service for a week, including the use of your phone as a hotspot and unlimited 128K data if you consume your 5GB allotment. ← actual plan found on eSIMdb at time of this writing. No contracts, no credit checks, typically up and running in a couple minutes.

Fail-over: you have a dual-SIM device and are frequently in an areas where your main carrier doesn't have service. You can load a PAYGO eSIM in the second slot, activate it, and let it fill in with the other two main carriers when needed. When your main carrier comes back on line it will revert to that cheaper solution.

SIM cards are the traditional ones you know and either love or hate. You buy one in a store or have it mailed to you, then you can put it in your phone. They can be swapped between devices.⁴⁾

eSIMs are

… a form of SIM card that is embedded directly into a device as software installed onto an eUICC chip. – Wikipedia

The advantage is you don't have to wait to get a card and normally don't have to divulge personal information to buy and use a profile. Apple has supported eSIMs since about iPhone 11. On Android phones the feature is fairly recent on more upscale models. Note: you can add eSIM functionality to any device using a physical eSIM (see below).

A physical eSIM is a mix between the two – the eSIM magic is embedded in a normal-looking SIM card. They have some advantages:

• they can add eSIM functionality to a device that does not natively support eSIMs
• they can store multiple eSIM profiles on the same card, and choose between them at will
• they facilitate transferring the eSIM to a different device

You will have to use mail or a store to procure the physical eSIM but after that it will be used over the internet like a regular eSIM module in a phone.

The main disadvantage of eSIMs in general is an internet connection is required to get the eSIM profile downloaded. A bit of a Catch-22 if one didn’t plan ahead. For this reason the makers of physical eSIM cards often preload it with just enough data⁵⁾ to get you through the purchase and activation.

• activation - this is when the profile becomes functional and any “X days of service” timers start. Depending on the device and provider this may be automatic. Also see installation.
• breakout - the geographic exit point where your data reaches the internet. It could be
  • local breakout - your internet IP address will be in the country or state where you are using it; this is generally preferable.
  • remote breakout - for economic, contractual or other reasons your IP may be geolocated in the UK, Asia, or Europe. Common recent examples would be Hong Kong or Poland. Remote breakout could make latency ⁶⁾ or connection speed worse. Some services (notably ChatGPT, Uber, or encrypted comms) may be firewalled in that country.
• installation - downloading the profile from the provider into the eSIM. This is most often done with a QR code that is emailed to you or shown on the website or app. The profile will not be usable until it is subsequently activated (see above).
• latency - delays in the transmission of data expressed in milliseconds. Increased latency usually affect small transmissions more than larger ones.
• local network operators - the network of towers you are actually connecting to. In the U.S. this would usually be one more of AT&T, T-Mobile, or Verizon. You will only be connected to one of them at a time. When multiple options are present the profile will choose the “best” one based on strongest signal or some other metric. In some cases you may want to manually choose a network to get optimal results.
• local plans - a plan that is valid only in one country. There are also multi-country, regional (Europe, North America), and global plans.
• pay-as-you-go (PAYGO) - an account with a defined BG limit but no time limit.
• profile - account and technical information about a data plan from the provider. Downloading the profile onto the card is called installation.
• provider - a company that brokers and sells plans for use with eSIMs.
• throttling - a limitation on speed you would otherwise experience. This can be no big deal (the throttle is higher than your normal use), annoying (5 day 5GB plan might only allow 1GB of fast data per day, then throttle thereafter, or a Good Thing (as when you get “free” throttled data after your GB allotment is consumed.

You can buy from one company or mix-and-match to find the best fit for a particular use.

• popular sellers
• information aggregators - these sites list hundreds or thousands of plans which you can narrow down by various filters. Their revenue comes from referral links to the listed providers.
  • eSIMDB - most common site for finding eSIMs from multiple providers.
  • eSIMradar - more filters but site functionality can be spotty
  • esim.guru - minimal filters available

• to use eSIMs the phone must be unlocked (not restricted to one carrier). Subsidized phones are usually locked for a certain time until the telco has broken even on giving you the phone.
• patterns in pricing - although there is extreme variability in pricing there are some general patterns
  • plans with multiple local network operators tend to be more expensive than plans with a single operator
  • plans with Verizon coverage tend to be more expensive
  • plans with longer expiration times tend to be more expensive by the GB. 5GB with no expiration would be most expensive, then one year, then one month, then one week, then one day being the cheapest. So focus on plans that closely match your expected time of use. Example: if you need only 7 days then buy a 7 day plan rather than a 30 day plan.
  • plans with multiple country coverage tends to be more expensive by the GB. Global plans would be most expensive, then multi-country, then single-country being the cheapest. So if you will only be in one country focus on single-country plans.