My iPhone always seems to jump to voicemail before I answer it. I need to increase the call forward delay. By increasing the delay before the call is transferred to voicemail, I have a better chance of grabbing it. As expected, the caller will hear an increased number of rings before being transferred. Works to decrease also. Google voicemail picks up at 25 seconds.

This requires a little friendly hacking. Call your iphone now from a different line to judge how long it takes to hit voicemail. 

1. dial the following: *#61# 
2. Press the Call button 
3. Write down your voicemail number. It's the number after "Forwards to" 

4. From the keypad dial the following: *61*1VOICEMAILNUMBER*11*30# inserting your voicemail number where VOICEMAILNUMBER is. It should be 11 numbers. 

(For example, if your voicemail number is 16787641111 then your command would be:*61*16787641111*11*30#) 

30 is the length of time in the command above. 20 is the default. 30 is the max. 

5. Press the Call button to send your command

6. You should see the following: 

Setting Activation Succeeded 
Voice Call Forwarding 
When Unanswered 

7. Congrats. You are set! Call your iphone again to see that it now takes longer to hit voicemail. 

If you screw up your phone, don't blame me. Do this at your own risk. If you want to be super safe, you can call AT&T and they will do this for you as well.

I used the method above to increase the time-before-forwarding-to-voicemail to 30 seconds. It worked!

  Turn Data Roaming "OFF":
By default the setting for international data roaming will be in the "OFF" position.
To turn data roaming "ON/OFF" tap on, Settings>General>Network>Data Roaming
  - Turning "OFF" data roaming blocks email, browsing and downloads, but it will not block text or picture/video messages.

- When abroad, international roaming rates apply when you send text or picture/video messages.

Utilize WiFi Instead of 3G/GPRS/EDGE:
WiFi is available in many international airports, hotels and restaurants to browse the Web or check email.

Turn Fetch New Data "Off":
Check email and sync contacts and calendars manually instead of having the data pushed to your iPhone automatically. This way you can control the flow of data coming to your iPhone.
    To turn off the Auto-Check functionality tap on
Settings>Mail, Contacts, Calendars>Fetch New Data, Change Push to "OFF" and Select to Fetch Manually

Consider Purchasing an International Data Package:
If you are traveling outside the U.S., purchasing a Data Global Plan will significantly reduce the cost of using data abroad.

Reset the Usage Tracker to Zero:
When you arrive overseas access the usage tracker in the general settings menu and select reset statistics. This will enable you to track your estimated data usage statistics.
    To reset Usage Tracker to Zero tap on
Settings>General>Usage>Reset