Not legally. Where I'm from they sold off the old 3G spectrum and frequencies, mostly (all?) to established telcos to use in 4G or 5G mobile services. They will not be happy if you start interfering with their customers there (especially not after the money they spent at the auction for those licenses).
There are some weird bits of the 900MHz band that cross into the fairly free-to-use ISM bands in some countries, and I recall a CCC talk where someone demonstrated a SDR setup doing mobile phone base station stuff by sneaking into what were ISM bands in Germany where he was that handsets would talk to because they were allocated as cellular phone spectrum in other parts of the world. Here in Australia we are limited and can't use the upper end of the 920MHz ISM band with LoRa devices, because Optus bought that spectrum for their phone network.
(Here in Aust4ralia we have other cellular spectrum and phone network problems, where a lot of older devices that support some 4 and/or 5G cannot reliably call 000 (our equivalent emergency number to the US 911), because the fall back to 3G when roaming onto other networks... A few people have died recently, and all the telcos are busy blocking a growing list of phones, mostly older Samsung ones if the noise in mainstream media here is accurate. I know my old but still otherwise functional Galaxy S6 Edge is not on the banned list.)