WORK IN PROGRESS All of them were downloaded from the Polish file hosting service Chomikuj.pl (Wikipedia). The old version with Era and Plus wallapers -> (click)
Era (not added yet)	Orange (not added yet)	Plus (not added yet)
Heyah (since 2004, Wikipedia) The first wallpaper, in 128x160px resolution, was reuploaded multiple times from 2008 to 2013. It's the only one from this brand where I can confidently say is official. The next four wallpapers in the resolutions 128x128px, 128x160px, 149x191px and 176x220px. They were uploaded to Chomikuj during the same time period, but only once or twice each. Generally speaking, Heyah is a prepaid mobile brand originally marketed toward teenagers and young adults, known for its edgy ads. In 2022, it shifted its target audience to the Ukrainian minority in Poland.
T-Mobile (since 2011, Wikipedia) Four GIFs available in two resolution sets: 128×160px and 240×320px. These were uploaded multiple times between 2010 and 2012. Interestingly, they appeared on Chomikuj a year before the rebranding. In 2010, the network was still known as Era (one of Poland's major mobile brands during the 2000s) operated by Polska Telefonia Cyfrowa (Polish Digital Telephony). In 2010, the PTC was acquired by Deutsche Telekom, and in 2011, the Era brand was replaced by T-Mobile as part of an international brand unification. Later, in 2013, Polska Telefonia Cyfrowa was officially renamed to T-Mobile Polska S.A. I still remember how my mom was unhappy with that change, because the new offer had worse terms of use (according to her), so she moved her number to Plus. The images on the left were used as (non-looping) startup screens, while the ones on the right were probably screensavers.
Play (since 2007, Wikipedia) Two sets of four wallpapers in 176x220px an 240x320px respectively, uploaded a few times between 2009 and 2013.