I use a permanent Skype-In phone number. This is a USA phone number that I pay skype for, it goes to voicemail if I am not online on Skype. I have the option of forwarding it to any phone number in the world, I pay the costs for any forwarded call from the USA at Skype rates.
So I pay about $66 per year for that Skype-in number plus unlimited free calls to the USA and Canada from abroad.
I do not give out my local number, just that USA number. I do not forward it when I am in Asia due to the time difference, but I get an email whenever someone calls it and I can then check voicemail through Skype.
When I was in Colombia, for instance, I got a call from my credit card company about a suspicious transaction. It was just me, I had just purchased an air ticket to Asia. Anyway, they had just called my USA number which forwarded to my Colombia cell, they had no idea where I was.
After I buy a new sim in a country, I just go to the Skype web site to enter in the new forwarding number for my Skype In number.
You can text to any number from Skype (not free) but the receiver cannot reply. So I started using a free program called TextFree on my Ipod Touch. They give you a USA phone number, with the area code of your choice, to text to and from, and the texts are free. All I need is a WiFi connection (and would work on Iphone with a WiFi or 3G data connection). So far, this has worked fine for texting back and forth with USA numbers from abroad.
The solution one chooses depends on how long you will be abroad, how much you want to spend, the hassle factor, etc. When I was in the Philippines, I found the internet infrastructure to be poor so using Skype for international calls was more of a pain.