Something that I have been playing with recently is Google Voice. It doesn't necessarily save you money but it can make life a little easier.
Here's how it works - you sign up with Google Voice - it's free. You choose a phone number (a different number from your regular number). You assign regular phone numbers to that number - so, for example, I put my office phone, my home phone and my cell phone on it. When someone calls that number, it rings all the phones, so no matter where I am, they get in touch with me without having to call around. I addition, I can program it so that it only rings certain numbers on certain days of the week or times of day (no point ringing my work desk number when I know I'm not going to be at work!).
I haven't done this last part yet, but when I get a unlocked phone for travel and buy a local SIM card, there's no reason why I shouldn't be able to put that number into Google Voice and then folks won't have to remember a new number, they can call me at the usual Google Voice number. I can turn off phones that have roaming charges, too.
The service has texting/SMS and voice mail.
So far I have been very impressed with this. Has anyone else had any experience using this, good or bad?