The straight answer to "roulette call bets" is found at the wheel. Roulette looks like pure chance, and it is, but the rules still decide how much any bet costs. A European wheel has one green zero, an American wheel adds a second, and French tables add rules that return half of some losing bets. Knowing which wheel is in play, what each bet pays and what the zero takes is most of what there is to know about playing roulette sensibly.
Licensed roulette wheels are not rigged: they are tested and balanced, and casinos log results so that a biased wheel would show up in the numbers. Balls are not weighted; they are made to a standard size and material, and a worn wheel is replaced rather than exploited. Roulette machines use a random number generator that is checked in the same way and cannot be fixed by the casino. Under licensing regulations there are no illegal bets on the layout itself, although devices that try to predict the ball are banned nearly everywhere.
The best odds in roulette are on a single zero wheel, and better still under French rules. European roulette keeps an edge of about 2.7 percent; French tables add la partage, which gives back half the stake on even money bets whenever zero lands and so halves that edge on those bets. French layouts also take call bets placed by name, such as the neighbours bet on a number and the two either side of it on the wheel. Knowing how to play French roulette mostly means knowing these extra rules.
When zero lands, la partage gives back half of any even money stake, so each of those outside chances costs the player half what it would on an ordinary single zero table.
Call bets are placed by name on French layouts; the neighbours bet covers a chosen number plus the two pockets either side of it on the wheel.
On a single zero wheel the chance is one in thirty seven, and on a double zero wheel one in thirty eight for each green pocket.
Choosing a single zero wheel, holding to a fixed budget and knowing when to stop is the only approach that works, since the edge stays constant.
Licensed wheels are tested and balanced, results are logged so bias would show, balls are made to a standard, and electronic machines use checked random number generators.