I use localphone.com.

• I use them mainly to make long-distance calls to Canada. Their rates to Canada are very reasonable.
  
• They allow no-PIN dialing, just like many of their competitors.

kukukajoo, about your needs:

• Localphone lets you send international SMSes that will look like they were sent from your cellphone. I don't know what they send for outgoing Caller ID on voice calls. I wonder exactly what you meant when you said people have to be able to reach you.

Some disadvantages of Localphone:

• Rates sometimes differ depending who you're calling within a country. This even applies to calls to the US. Most calls to the US cost 0.5 cents per minute. But for calls to certain numbers in the US, Localphone charges 3 cents per minute instead. And if you dial one of those certain numbers, the Localphone voice menu system doesn't warn you in advance before the call is connected. The only way to get advance warning is to type the destination number into the rate calculator before you make your call. See the rates page.
  
• AFAIK they don't have a toll-free access number in Canada or the US.

And as with many third-party LD carriers:

• They don't have local access numbers in every city in my province, so when I travel to the countryside, their nearest local access number is often no longer a local call for me.
  
• They do not play any advice-of-charge message before they connect you ("This call will cost XYZ cents per minute"). So if you accidentally call a friend's cellphone instead of their landline, you could suffer bill shock. If you want advice-of-charge messages, consider Google Voice instead.
  
• Having to dial a local access number is a bit inconvenient than direct dialing. But there exist apps that will help you with this, at least for iPhone and Android.
  
• If you live in certain places, you'll pay your wireless carrier a high per-minute rate for incoming LD calls. I live in Canada. My carrier, Telus Mobility, charges me IIRC 35 cents per minute.