Thanks for visiting FixYa!
I'm familiar with the Tandy 43-165 sold by Radio Shack. It is one of the few phones ever made that has a headset jack built in. (Which is very rare.)
First, I'm going to give you the link to review your User Guide (just in case you don't have one.)
http://www.radioshack.com/graphics/uc/rsk/Support/ProductManuals/4300165_PM_EN.pdfI've tried to remember if the phone has the option to choose the number if rings before the call is diverted to Voice Mail. (I don't believe it does) But if it does, on the top 2 rows (of 5 buttons) the option would be located by pressing the (up) or (down) arrows. If the option is available, select the number if rings then press the OK/C button to confirm.
If no option exists for the number of rings - and you have an answering machine - the option may be with your answering machine.
Next step: If neither of the two options mentioned above work - try unplugging your phone and plugging another one in its place. Then, call your phone and see if the other phone rings MORE than once. If it does, the problem is with your Tandy 43-165 and it may need to be repaired or replaced. If the other phone ONLY rings once - then goes to Voice Mail - go to the next step.
If you use voice mail as part of your phone service, contact your service provider and request Tech Support. Note: I wouldn't mention that you think the problem is with your phone. Instead, simply inform Tech Support that you only receive one ring before the call diverts to Voice Mail and you may need them to re-set your voice mail account.
When setting up your voice mail after re-set, check to see if there's an option for the number of rings before the call is diverted.
In short, I believe the problem may not be with your Tandy phone - but, by trying another phone in its place, you'll find out quick enough.