SIM-Free Mobile Phones

Type

• Smartphones - run operating systems, so they are actually small computers. In addition to calling, messaging and photography, you can browse the Web and play games.
• Push-button telephones - suitable only for calling and SMS messages. As they have no operating system and a smaller display, their batteries last several days without a recharge.
• Phones for seniors - special push-button phones that feature easy-to-read displays and large buttons. They very simple to operate and often come with handy features such as FM radio, flashlights, or SOS buttons.
• Durable phones - feature improved impact resistance, and often resistance to dust and water.

Display size

• 3.9" and less - small screen, found on push-button phones.
• 4" to 4.4" - a very compact phone, perfect for one-handed operation.
• 4.5" to 4.9" - a balance between display size and compact dimensions.
• 5" to 5.4" - a popular size suitable for watching movies, playing games and surfing the Internet.
• 5.5" and more - devices on the border between phone and tablet (phablet).

Operating memory

• Less than 1 GB - for basic use only (a few simple applications or games).
• 1 GB - for undemanding routine use (active internet use and multiple applications).
• 1.5 gigabytes - for smooth running of the operating system; you can surf the Internet or play less demanding games.
• 2 gigabytes - for comfortable Internet browsing and playing games; sufficient for multiple concurrent applications.
• 3 GB - for smooth running without jamming even during multiple processes.
• 4GB or more - able to handle multiple demanding operations; will satisfy the most demanding users.

Storage space (internal memory)

Part of a phone's storage space is already taken up by the installed operating system and related programs. So you will not have the full value available, but several GB less. The exact number varies according to the specific product and manufacturer.

• 8 GB - sufficient for several applications and small amounts of music.
• 16 gigabytes - for undemanding users; sufficient capacity for several applications and music albums.
• 32 gigabytes - for dozens of applications and normal everyday use; sufficient for most users.
• 64 gigabytes - holds dozens of applications, games or music albums, several films.
• 128 gigabytes - holds hundreds of applications, games and dozens of movies; suitable for intensive use.
• 256 gigabytes - holds dozens of movies, games and applications; for the most demanding users.

Battery

• Capacity - measured in mAh. Ordinary smartphones have approx. 2500 mAh. Higher capacities are usually found on models with larger screens, which provide more space for hiding the battery.
• Batter life - not only determined by the battery capacity, but also how you use your phone, as well as the energy performance optimisation of the hardware and operating system. Smartphones generally last between one and two days. Despite their lower battery capacity, push-button phones have much longer battery life (over a week).

Camera

• Resolution - excellent image quality can be achieved by mobile phones with 12-megapixel cameras, whereas 5MP is sufficient for front-facing selfie cameras. Image quality also depends on the quality of the lens.
• Maximum aperture - specifies the maximum amount of light that the lens can let through. A value below f / 2.0 is considered excellent.
• Optical image stabilisation - allows you to capture images without blurring, even when moving. 
• Software image stabilisation - not image stabilisation in the true sense of the word; by increasing the ISO sensitivity, sharper images can be achieved. It is not, however, as effective as optical image stabilisation.
• Focus - some smartphone cameras focus at a short distance with the aid of a laser, while others do so by means of phase-detection auto-focus (PDAF). The best devices use a combination of both methods. For iPhone variations, PDAF is known as "Focus Pixels".
• Dual camera - provides improved focus options and increased luminosity; allows you to change the focus area and adjust the depth of field. The capabilities and functions of a dual camera differ from model to model.