same here for several years already on my venerable FxTec Pro1 : no dial tone, but just with one single company, that's rebtel.com, and usually only when my phone wasn't rebooted recently. if freshly restarted everything works as expected : LED, ringing, dial tone, alarm tone, volumes. but the longer it's up, frequently months in my case, the likelier it becomes that these functions somehow misbehave or go dead even...
i think it's in parts also an issue with the installed Android issue, it's just not the same as a proper linux system, like my rock-stable Slackware boxes.