For context for this, Twilight is a runaway without a purpose. Failing her Magic School test, unable to even do a simple spell she quit doing magic all together. Living alone on the run with a small trailer she got, she attempts to find her purpose with no progress.
During one of her trips from city to city, she comes across a pink unicorn cloaked like herself. Unlike her though she is very talkative to her, which Twilight doesn’t really like. Eventually the Unicorn follows her out of that city and basically travels with her in attempt of the Unicorn (Who introduced herself as Sunbright) to befriend her
In actuality, Sunbright is actually Princess Celestia herself following around the pony she believes is the bearer of one of the Elements of Harmony. Forced to flee Canterlot after it was revealed that Nightmare Moon would be free again, being unable to use the Elements due to them finding a new bearer set out to find them. She ran into Twilight purely by chance and detected something about her. While Twilight has never shown any magic ability, something about her seemed far stronger than she lets on. Celestia has been attempting to befriend and bond with Twilight in hope of helping her show off that magic she has deep within.
The Magicial Tin Can Phone is kinda meant to represent that attempt to reach out to Twilight, not answering her calls. I was also listening to Telephone by Lady Gaga while drawing it soooo yeah