If you want to try to grow your own solution, the ICs I have are TP5089N. They look quite handy for this sort of purpose.
They require very little other than a 0-9 + *, # keypad (widely available) + a common 3.57Mhz crystal. They run from a very wide supply voltage range. It would be up to you to make the interface between the IC output and the line.
If you think they might be any use, PM me and I'll bung you a couple along with matching 3.57Mhz crystals.
http://www.repeater-builder.com/tech...mf/tp5089n.pdf