So, Apple didn't include a lot of countries in Address Book. That's mean you can't add Address with unsupported country like my. I'm from Latvia. Where is my country? What can you do?You have jailbroken iPhone/iPhone 3G with firmware 2.1. Connect to iPhone/iPhone 3G. Go to:
/System/Library/Frameworks/AddressBook.framework
download file: ABAddressFormats.plist
You can edit with TextWrangler.
There is small example for my country Latvia.
Latvia specific code is: LV
find correct place and add like that.
<key>lu</key>
<dict>
<key>COUNTRY</key>
<string>Luxembourg</string>
<key>City</key>
<string>City</string>
<key>Country</key>
<string>Country</string>
<key>EDIT_FORMAT</key>
<string>Street
Street2
ZIP City
Country</string>
<key>FORMAT</key>
<string>Street
ZIP City
Country</string>
<key>PHONETIC_COUNTRY</key>
<string>Phonetic Luxembourg</string>
<key>Street</key>
<string>Street</string>
<key>URL_FORMAT</key>
<string>Street, ZIP, City, Country</string>
<key>ZIP</key>
<string>PostalCode</string>
</dict>
<key>lv</key>
<dict>
<key>COUNTRY</key>
<string>Latvia</string>
<key>City</key>
<string>City</string>
<key>Country</key>
<string>Country</string>
<key>EDIT_FORMAT</key>
<string>Street
Street2
ZIP City
Country</string>
<key>FORMAT</key>
<string>Street
ZIP City
Country</string>
<key>PHONETIC_COUNTRY</key>
<string>Phonetic Latvia</string>
<key>Street</key>
<string>Street</string>
<key>URL_FORMAT</key>
<string>Street, ZIP, City, Country</string>
<key>ZIP</key>
<string>PostalCode</string>
</dict>

<key>mk</key>
<dict>
<key>COUNTRY</key>
<string>Macedonia</string>
<key>City</key>
<string>City</string>
<key>Country</key>
<string>Country</string>
<key>EDIT_FORMAT</key>
<string>Street
Street2
City ZIP
Country</string>
<key>FORMAT</key>
<string>Street
City ZIP
Country</string>
<key>PHONETIC_COUNTRY</key>
<string>Phonetic Macedonia</string>
<key>Street</key>
<string>Street</string>
<key>URL_FORMAT</key>
<string>Street, City, ZIP, Country</string>
<key>ZIP</key>
<string>PostalCode</string>
</dict>



Save document and upload back.You can restart phone...
Works great now with Maps.app