Question about Skype subscription
 

Can an unlimited US/Canada Skype subscription w/ Skype In number be used outside of North America? If so, would it make sense to take advantage of mobile data for Skype uses? One could for instance, use Fring to make calls over WiFi or 3G (or even 2G) and only pay the annual fee to keep the number & Skype subscription going, resulting in cheap placing & reception of calls to the US or Canada from many other places.

Considering that I never hear of this, I'm guessing Skype doesn't allow it?

If you already use Fring, which fully supports SIP (the major VoIP-protocol), why don't you just look for an American VoIP-provider with free DIDs instead of paying for Skype?

Free DIDs - don't I still need to pay for whatever calls go through them? Are there any reliable providers that has something that is practically unlimited use for a flat monthly or annual fee (like the way Skype charges)?

No, there are some VoIP providers, that will issue an American DID number completely free of charge - no set up fee, no monthly fees, no charge for talktime.

Perhaps the best choice would be poivy.com - they will give you nearly unlimited outgoing calls to North American numbers and to landlines in a couple of other countires in the Western World for 90 days if you just add some € 10 to your account. Those € 10 will actually not expire after those 90 days, but this amount will remain in your account and you can use it for non-free destinations. After those 90 days the originally free destinations will be charged with a still cheap tariff of € 0.015/min. The same price will apply if you exceed 300 minutes of calls to free destinations per week during the freedays-period.
Practically poivy gives you free calls just as a bonus for adding credit, which you may or may not use for calls to non-free destinations.
If you recharge another € 10, you will get another 90 days (which will be added to your remaining freedays, if such are left).
I'm phoning for 4 years with poivy now, and since I usually spend those € 10 on calls to (European) mobile numbers and international destinations before those 90 days elapse. Due to the subsequent recharges I never run out of freedays and even I did, those € 0.015/min would still be a bargain if you consider those 90 days of free calls you had before.
Also they will give you a free US DID number for a one-time fee of € 1, that will never expire.
Sounds very complicated, but it's by far the cheapest I've discovered in 5 years, that I'm using VoIP only instead of a regular landline and they are highly reliable and the voice quality is perfect. There's no difference compared to a regular phone if you use appropriate equipment.
Further poivy also has a callthrough and (a webtriggered) callback service and you can send SMS very cheap through their website.

try www.sipgate.us to get a free us sip number. Not all number ranges are available for free altough.

I didn't know sipgate established operations in the US. Having used sipgate.de as primary provider for inbound calls for 5 years now, I can recommend their service implicitly. Unfortunately they have blocked their price list for users from outside the US and so I can't see their rates, but I assume poivy.com still has cheaper rates than sipgate.us - so if you intend to place outgoing calls regularly, poivy.com may still be the way to go.