Trade (or Lot) sizes start at 0.1 (a 10,000 unit trade or 10,000 base currency size) up to lot sizes of 1 (a 100,000 unit trade or 100,000 base currency size) per one lot.
Here are some examples of what this means:
U.S. Dollar/Japanese Yen (100,000 U.S. Dollars)
Euro/U.S. Dollar (100,000 Euros)
Euro/Great Britain Pound (100,000 Euros)
Euro/Japanese Yen (100,000 Euros)

Put simply, margin serves as collateral to cover any losses that you might incur. Since nothing is actually being purchased or sold for delivery, the only requirement, and indeed the only real purpose for having funds in your FX account, is for sufficient margin.
Essentially when you trade on margin you are using a free short-term credit allowance from JMI Brokers Limited. This short-term credit allowance is used to purchase an amount of currency that greatly exceeds your account value.

Let's take the following FX example:
You have an account with $10,000 with JMI. You trade ticket sizes of 1,000,000 GBP/USD. This equates to a margin ratio of 1% ($10,000 is 1% of $1,000,000). How can you trade 100 times the amount of money you have at your disposal? The answer is that JMIS temporarily gives you the necessary credit to make the transaction you are interested in making. Without margin, you would only be able to buy or sell tickets of $10,000 at a time. On standard accounts JMI Brokers applies a minimum 1% margin.
This margin facility allows you to potentially make large profits from a relatively small initial investment but it must be pointed out that any losses are equally multiplied.
Customers who hold FX positions may become liable to pay margin as detailed in our terms and conditions. All FX positions have an initial margin and you are required to keep this over and above any unrealized losses. Margin calls can be made at any time and it is therefore important for you to familiarize yourself with our terms and conditions especially the section relating to margin calls. Be aware that it is your responsibility, not JMIS, to monitor your positions and make any margin payments as they become due.

Our FX trading platforms have been designed to effectively monitor and allow you to control risk exposure in real time. Based on each clients margin requirement, the FX trading platform system calculates both the funds needed to retain current open FX positions and the trading resources available for entering into new positions or for adding to existing open FX positions.
If the equity in your account drops below the margin required to maintain your open positions, we may close all open positions. Once usable margin reaches zero, a margin call will ensue, and all open positions may be closed by us. This limits your risk to usable margin.