Yes, that's correct. For tax purposes, LLC can be treated as only one of the two: Sole Proprietor OR Partnership. In order to be a Partnership LLC it needs to be more than one individual, and tax rules are better. That's my limited understanding so far.
Here is a quick article explaining it:
"Have you started a small business and need to know when to file your tax returns? Perhaps you've heard about filing quarterly returns and are wondering if that requirement applies to you? Read on to get answers to these important questions.
Annual Income Tax Returns. All small businesses must file a return annually. Generally speaking, if your business has a calendar year-end, you must file one of the following business income tax forms by the due date listed below:
Sole Proprietorship - Schedule C, as part of your personal return, is due April 15. Partnership - Form 1065 is due April 15. C Corporation - Form 1120 is due March 15. S Corporation - Form 1120S is due March 15.
Limited Liability Companies (LLC) get their own special explanation, for they are a unique business entity. An LLC can be taxed like any of the above-mentioned entities. However your LLC is treated for tax purposes determines the appropriate tax form and the accompanying due date.
Quarterly Tax Returns. Here there are two possibilities. First, if you are a self-employed sole proprietor who files Schedule C as part of your personal return, you may be required to make quarterly estimated income tax payments via Form 1040-ES. This is probably what you have heard about when people talk about "filing quarterly taxes".
These quarterly payments are due April 15 (first quarter), June 15 (second quarter), September 15 (third quarter) and January 15 (fourth quarter). The purpose of these payments is to comply with our federal "pay as you go" tax system. The payments are for both federal income taxes as well as self-employment taxes. Failure to make these payments can result in a penalty for underpayment of estimated tax payments, even if you pay your balance due with your return on April 15. So be sure to determine whether you must make quarterly estimated tax payments.
A second type of quarterly return you may have to file are for payroll taxes. If you have employees, you must issue paychecks and withhold taxes from those paychecks. Those payroll tax withholdings must be paid within a certain timeframe, depending on the amount. And there are also federal payroll tax returns that must be filed. The most common one is Form 941, which must be filed within one month after the end of each calendar quarter (April 30, July 31, October 31, and January 31).
If you have no employees, you don't have to deal with payroll and the small mountain of paperwork that accompanies it. Many sole proprietorships and partnerships fall into that category. But if you are a corporation (or an LLC taxed as a corporation), and you are performing services for your business, you must pay yourself reasonable compensation as an employee of your business, and therefore will be required to issue yourself paychecks and file the resulting quarterly payroll tax forms."
Do You File Business Tax Returns Quarterly or Annually? — Business Management Daily: Free Reports on Human Resources, Employment Law, Office Management, Office Communication, Office Technology and Small Business Tax Business Management Daily
So basically if you open an LLC, you have a choice as to what tax entity it's treated as. It doesn't make sense to use it as a corporation, because then you have to abide by the quarterly rules that corporations have to file. I believe Sole Proprietors have similar quarterly rules, but if you use partnership structure, you don't have to file anything but your yearly taxes and yearly articles of incorporation for the LLC.
Re: Re-use EIN? 
