For the current week, the overall ratings of three Diversified Telecommunication Services stocks are worse, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Elephant Talk Communications Corp. (AMEX:ETAK) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Elephant Talk Communications provides voice, data transmission, pre-paid calling cards, and Internet service provider services. In Portfolio Grader’s specific subcategories of Earnings Momentum, Equity, Cash Flow, and Sales Growth, ETAK also gets F’s. To get an in-depth look at ETAK, get Portfolio Grader’s complete analysis of ETAK stock.

China Telecom (NYSE:CHA) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. China Telecom is an integrated information service provider that offers telecommunications services, including wireline voice services, mobile voice services, and Internet access services. For a full analysis of CHA stock, visit Portfolio Grader.

Oi (NYSE:OIBR) earns a D this week, falling from last week’s grade of C. Oi provides integrated telecommunication service for residential customers, companies, and governmental agencies in Brazil. The stock also gets an F in Margin Growth. For more information, get Portfolio Grader’s complete analysis of OIBR stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.