
In the article I will not explain what VoIP is, how to configure the client program (usually all the data is on the provider's website). I’ll dwell only on PC clients and VoIP services.
Windows clients
X-Lite (Free)
Bria (Paid, from the same company)
Differences: In the second, you can set several SIP providers, and make and receive calls to all configured accounts.
Both clients are fast and easy to set up.
Linux clients
I use ekiga, and everything suits.
')
Mac clientsPrompt in the comments
VoIP Services
Immediately stipulate - I give all prices in rubles. Course on the day of the post: € = 44.71, $ = 31.05
In general, all providers are similar, but there are some differences.

Perhaps the most famous sip-provider of the RuNet.
Features
A large number of instructions to configure clients
Convenient account replenishment
The possibility of ordering a call (at a double rate)
Most of the devices on the Russian market have been approved by the provider

You can find out the price of the direction you need here:
http://www.sipnet.ru/orderandpay/tariffs.phpMy opinion:
Price: ■■■ □□
Quality: ■■■■ □

Features
The price is 1 ruble for all calls in Russia (yes, and mobile).You can start to call only after making 200 rubles to the account
Payment is quite convenient (credit cards, online money)
SMS callback and just callback
The ability to call from a city number to sip (dial +74995034004, and then the internal number of the subscriber)
Instructions for setting up only one PC program, not to mention hardware
Support service operator works up to 19 hours
My opinion:
I tried to use it myself, translate a girl from Skype - everything pleases, except for the quality of communication. Constant gurgling, disappearing, interference, rattling on both sides. Codecs no matter how changed - does not help.
PS In the comments on the quality of communication, however, do not complain.
Tariffs here.
Price: ■■■■ □
Quality: ■■ □□□

Features
Interface in English
You can put any Caller ID without authentication
Payment only through Google Checkout or Paypal
Tariffs are among the lowest.
My opinion: Inexpensive, not audible perfect, but acceptable.
Price: ■■■■ □
Quality: ■■■ □□

Features
They give 200 minutes a week free of charge in the main areas (in Russia - local SPb and MSC numbers) , but only after making a prepayment (any)
Register only after installing special software.
After 200 minutes a week:

This service is a clone site of the company Betamax (they still have about 20 sites, the prices are identical)
It is convenient to pay via the website betamax.ru
Tariffs are very attractive.
My opinion: 200 free minutes a week is very cool, the quality is normal, above average.
Price: ■■■■■
Quality: ■■■■ □
Features For comparison

Convenient customer
Video calls
Very popular
High quality of communication, even when calling to landline numbers.

My opinion:
Price: ■■■ □□
Quality: ■■■■■
PS Soon I will publish the review of the VoIP-Dect of the SIEMENS C470IP phone - it supports work with 6 voip-providers and the usual analog line.
Good and cheap communication!