When one of the long distance discounters comes to your city or town, look before you leap, suggests Joe Waz, deputy director of the National Citizens Committee for Broadcasting.
Mr. Waz, who wrote a telephone guide, ''Reverse the Charges'' for the nonprofit consumer group in Washington, D.C., suggests that consumers examine their long distance phone habits before making any decisions. Namely:
* What locations do you frequently call long distance?
The major disadvantage of the discounters is that they do not reach nationwide, company officials say. All of them reach 95 or more major metropolitan areas.
* How much do you spend on long-distance calls?
Since the discounters charge a subscription fee or have a monthly minimum charge, observers agree that callers who spend less than $25 per month on long distance do not benefit significantly, if at all.
* What time of day do you call long distance?
Waz says the greatest savings can be realized in the evening - before 11 p.m. when Bell drops its rates 60 percent. Besides its regular residential service, City-Call offers a flat-rate deal for calls on weekdays after 8 p.m. and on weekends and holidays. For a monthly $10 service charge, the first two hours worth of calls cost $5 (4.2 cents a minute). Every half hour thereafter costs $5 (8.3 cents a minute). That rate is good for any city served in their system.
* How long distance are your long distance calls?
If most are to nearby cities, Waz says, the customer won't save as much with the discounters. But the greater the distances, the greater the savings, he says.