This unit started shipping in 2004 from what I can find. At well over a decade I can't fault a maker for no support but there are folk that need life time support. I get that but it's very very old.
Try Ebay if it must be the same model.
I've got what must be a 8-10 year old Uniden DECT 6.0 2188 with a corded base unit/answering machine and three cordless handsets. The problem is the corded base unit loses receiving audio depending on the position I'm holding the corded handset, while the other person can hear me no matter what. I tried swapping cables, but it must be either in the connection inside the base or in the handset. Uniden no longer supports their phones, so unless someone has a suggestion for a DIY or other not too expensive fix, that leaves me with either getting a whole new phone system or finding a compatible corded base of similar type. I haven't found any 2188's, except with a bunch of handsets, which I don't need.
What I'm trying to figure out, short of trial and eror, is what Uniden base units with answering might be compatible with the 2188. Any ideas? Here's a link to the basic specs: https://www.101phones.com/details/13975/uniden-DECT2188-5.html. Thanks,