When typing on your iPhone/Touch you will run into the necessity to use punctuation marks. These are all located on the numbers portion of the keyboard. Instead of pressing the numbers key to get to the punctuation, selecting the mark and then having to change back to the letters portion of the keyboard, you can use a simple press, slide and select motion to select the punctuation and automatically go back to the letters.
When you need to insert a punctuation mark into your text, do the following:
Press and hold the Numbers key on the keyboard (the key with .?123 on it).
When the keyboard appears, slide to the desired punctuation mark and let go to select it.
The selected punctuation will appear in your text and the keyboard will automatically go back to the letter keyboard so you can continue typing your text.
For inserting periods, simply tap the spacebar twice, you don’t even need to access the numbers keyboard.