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”).

This week, Premiere Global Services (NYSE:PGI) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Premiere Global Services is a global provider of conferencing and collaboration services. The stock price has fallen 7.1% over the past month, worse than the 2.2% decrease the S&P 500 has seen over the same period of time. For a full analysis of PGI stock, visit Portfolio Grader.

This is a rough week for IDT Corp. (NYSE:IDT). The company’s rating falls to D from the previous week’s C. IDT provides retail and wholesale telecommunications services and products, including pre-paid and rechargeable calling cards and wholesale carrier services. Investors seem to agree with the downgrade and have pushed down the share price 9.2% over the past month.

For more information, get Portfolio Grader’s complete analysis of IDT stock.

Elephant Talk Communications Corp. (AMEX:ETAK) earns a F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). Elephant Talk Communications provides voice, data transmission, pre-paid calling cards, and Internet service provider services. The stock gets F’s in Earnings Momentum, Equity, Cash Flow, and Sales Growth. To get an in-depth look at ETAK, get Portfolio Grader’s complete analysis of ETAK 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.