What kinds of error codes are you receiving on your device? If you can supply me with your device model and the error code you're receiving I can provide you with a resolution.
i recently got samsung replenish about a month ago or so. love this phone but my recent problem is error code 128 with data username and password incorrect and 3g data service contantly going out although its not turned off. PLEASE HELP -- i even had it brought to Sprint kiosk store but now am asked to go to rochester or victor for more in depth repair
If you haven't tried it yet, try this.
Go to Settings > About Phone > System Updates > Update Profile
This *should* reprogram your data information allowing you to connect. If that doesn't do it, or if it errors out on that and you can't get it go through after a few tries, you may have to call in or visit that service center.