Mio A501 - Manual (Page 81)

Using the Phone
3-27
Dialing an International Call
When you are manually dialing a number, tap and hold the number 0 until the
+ sign appears. The + sign replaces the international prefix (00) of the
country from where you are calling.
Enter the full phone number you want to dial including country code, area
code (without the leading area code zero) and local phone number.