Analyst upgrades typically lead to positive short-term price movements as they reflect a positive outlook on the company's future performance. The upgrade from Peer Perform to Outperform suggests a strong confidence in AT&T's potential to outperform the market, which could attract more investors to the stock. The $21 price target further quantifies this optimism, indicating a specific value that the analyst believes the stock can reach, potentially influencing investor sentiment and stock price in the short term.