Photo credits

Open Line uses eighteen photographs. Seventeen were released under CC0 and one has fallen into the public domain, so all eighteen can be reused freely. Most came to us through Wikimedia Commons (several by way of Unsplash) and a single one through Openverse. Next to each guide you will find the photographer and a link to the original upload.

When a guide about roaming shows a departures board, or a guide about VoIP shows a network switch, the picture only signals the subject. The phones, masts and people in frame are not the services, operators or callers described in the text, and we are not promoting any handset, network or app.

Credits for each guide

• Opening photo on the home page: Three vintage pay telephones with rotary dials and coiled cords mounted in a row on a pale wall. Photo: Pavan Trikutam / Unsplash, via Wikimedia Commons (CC0 1.0).
• What is VoIP? How a phone call travels over the internet: Dozens of blue, yellow and green network cables plugged into a rack-mounted Ethernet switch. Photo: Raysonho (Open Grid Scheduler / Grid Engine) / Wikimedia Commons (CC0 1.0).
• Wi-Fi calling explained: how it works and how it differs from calling apps: Two hands holding a smartphone over a café table with a magazine and two cups of coffee. Photo: Maliha Mannan / Unsplash, via Wikimedia Commons (CC0 1.0).
• Why VoIP calls break up: latency, jitter, packet loss and how to fix them: Over-ear headphones lying on a dark desk beside a smartphone with a lit screen. Photo: wu yi / Unsplash, via Wikimedia Commons (CC0 1.0).
• How much data does a VoIP call use? The calculation, codec by codec: A hand holding a smartphone whose screen shows a grid of colourful app icons. Photo: bohed (Pixabay), uploaded by Océanos y dados / Wikimedia Commons (CC0 1.0).
• VoLTE and the 2G/3G switch-off: will your phone still make calls?: Aerial view of a lone mobile phone mast beside a country road, surrounded by green fields and a farmhouse. Photo: Wikideas1 / Wikimedia Commons (CC0 1.0).
• Calling abroad: roaming, local SIMs, eSIMs, Wi-Fi calling and apps compared: Close-up of an airport departures board listing destinations, departure times and flight numbers. Photo: Redolta / Wikimedia Commons (CC0 1.0).
• EU roaming rules: what "roam like at home" covers, and what it does not: A blue European Union sign marking the Slovenian border beside a road that passes under a bridge. Photo: Dantadd / Wikimedia Commons (Public domain).
• eSIM explained: how it works, which phones support it, and using it abroad: Diagram of SIM card formats from largest to smallest: Mini SIM, Micro SIM, Nano SIM and the tiny embedded eSIM chip. Photo: Jbond2018 / Wikimedia Commons (CC0 1.0).
• Keeping your number: porting, caller ID and spoofing when you call over the internet: Close-up of an old rotary telephone dial with a paper number card at its centre and a coiled cord beside it. Photo: Daria Nepriakhina / Unsplash, via Wikimedia Commons (CC0 1.0).
• Emergency calls over VoIP, Wi-Fi calling and apps: what works and what does not: A blue roadside call box sign on a pole with a small solar panel, beside a desert highway. Photo: Ruff tuff cream puff / Wikimedia Commons (CC0 1.0).
• Supported devices: what makes a phone work well (or badly) for internet calls: A smartphone with a dark screen lying flat on a pale woolly blanket. Photo: Astra.L / Wikimedia Commons (CC0 1.0).
• What calling and messaging apps actually encrypt (and what they still reveal): Three padlocks on a table: a brass key padlock, a brass combination lock and a small red combination lock. Photo: Mx. Granger / Wikimedia Commons (CC0 1.0).
• Moving abroad: keep your number, call home cheaply, and find a place to live remotely: An open grey suitcase on wheels, half packed, with a book and a striped scarf spilling out. Photo: rawpixel / rawpixel (CC0 1.0), via Openverse.
• Satellite texting on an ordinary phone: how direct-to-cell works and what it can do: A starry night sky with the Milky Way above a dark treeline, crossed by two bright streaks of sunlight reflected from passing satellites. Photo: Dylan O'Donnell / Wikimedia Commons (CC0 1.0).
• One-ring scams: why a missed call from an unknown foreign number can cost you money: A hand holding a smartphone whose lock screen shows the time and a purple wallpaper, against a plain grey wall. Photo: Oliur Rahman / Unsplash, via Wikimedia Commons (CC0 1.0).
• Calling toll-free numbers from abroad: why 0800 and 1-800 numbers fail, and what to dial instead: A row of wooden phone booths in the restored TWA Flight Center at JFK airport, two fitted with old black payphones, with a window onto the apron behind. Photo: Warren LeMay (w_lemay) / Wikimedia Commons (CC0 1.0).
• Hiding your caller ID: the codes that withhold your number, and who still sees it: A smiling bearded man in a dark suit and red tie holding a smartphone to his ear, against a blurred grey background. Photo: rawpixel / Unsplash, via Wikimedia Commons (CC0 1.0).

Open Line keeps every photo in two sizes, cropped to 3:2 and converted to WebP, without further retouching. If you took one of these pictures and the credit is wrong, tell us through the contact page.