From the author's README on Thunderstore

Swaps the smartphone your skater pulls out for a classic Nokia 3310: navy shell, grey keypad, green-grey LCD.

What it changes

characters/props/phone/basicsmartphone/basicsmartphone_mesh: the phone mesh, replaced with the Nokia
basicsmartphone_proxy_c / basicsmartphone_proxy_msk: the phone's own textures, repainted with the Nokia colours

It doesn't touch any shared materials, so nothing else in the game changes colour.

Install

Install with the ReSkate launcher, or drop the folder into Skate/Mods and enable it.

Credits

3D model: This work is based on "Nokia 3310" (https://sketchfab.com/3d-models/nokia-3310-ff7c87c59f10466abe76b481ad03b418) by SPD_3D (https://sketchfab.com/SPD_3D) licensed under CC-BY-4.0 (http://creativecommons.org/licenses/by/4.0/). Changes from the original: decimated, rescaled, recoloured and converted for Skate with ReSkate Studio.

Install Nokia 3310 Phone

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Nokia 3310 Phone and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.