Any SIP-enabled software (aka softphone or SIP client) will allow you to receive calls on a local or toll-free number. That's not a problem - there are lots of various free or commercial SIP clients out there (for example, X-Lite and , correspondingly). You can either download some SIP clients from providers' websites for free, or download from various software repositories (or buy commercial SIP software online).
Certainly, in order to successfully use that approach, your phone number should be configured on a provider's side. In VOIP terminology, such providers are often called SIP providers (note that using term VOIP provider is a bit confusing, since some VOIP providers do not use SIP as their main protocol, for example, Skype). Phone numbers, which your chosen provider(s) will be routing and terminating SIP calls to, are called DID numbers (DID is an abbreviation of "direct inward dialing").
There is a large number of SIP providers of various sizes, feature sets and quality. Since you have mentioned reliability as one of the main criteria, I would recommend you the following providers (I used them all): Callcentric, voip.ms and Anveo. Local US DID numbers are relatively inexpensive, with Anveo being the least expensive than the other two (for simple plans like personal unlimited or pay-per-minute - more complex (especially, business) plans require more detailed cost-benefit analysis).
Speaking of getting and using free DID numbers, here's what I know. Currently, you can do that either via Callcentric (they offer only New York State phone numbers for that program), or via IPKall - a service, which offers Washington State phone numbers only. Also keep in mind that IPKall doesn't offer customer service and is likely much less reliable than Callcentric. So, if you don't care about the area code of your DID number, I suggest going the Callcentric route. Their program is called "Free Phone Number" and you can find more information about it here. In case, if/when their free DID numbers program will be stopped, you should know about their another program, which offers US and Canadian DID numbers (certain areas) at a reduced price. This program is called "Dirt Cheap DID", has been around a while and you can find more information about it here. Please let me know, if you have any questions. I hope that this is helpful.