auto prefix dialing circuit

i live with my granny and so to phone use a seperate service that is actually cheaper but requires dialling a frefix. so can a circuit be made to be put before the phone to predial it at a press of a button automatically. or is it possible to hac the phone maybe a counter that will feed a decoder that at each beat will dial a number.
i need a general direction to go in.

Thunderchild said:

i live with my granny and so to phone use a seperate service that is actually cheaper but requires dialling a frefix. so can a circuit be made to be put before the phone to predial it at a press of a button automatically. or is it possible to hac the phone maybe a counter that will feed a decoder that at each beat will dial a number.
i need a general direction to go in.

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The companies usually supply such a device with the service?, we had such a service at work for a while, and they gave us a box for every phone. We don't use them anymore, and I took one to pieces - it's stuffed full of surface mount chips, including at least two PIC's - however, these were quite complicated ones, they automatically analysed each number and dialed the cheapest option regardless (they downloaded accurate data for this on a regular basis).

hm no they don't supply it as i can use this from any phone. it works like this. i pay and get a pin number. then i phone a green number and insert the pin and then can phone anyone. but i can also register the number i phone from so i just dial the prefix before every number. so i want to make a box that will dial the number when i press the button or i could make it work so that when the handset is raised it is dialed. i could as i said interface directly to the phones keypad but i'm not sure on how to electrically press the buttons. relays r obvious but large noisy power consuming and expensive (5 € here ridicolous)

Buy a cheap phone with 10 number memory, and store the prefix in mem1.

then what can i still dial another number after. perhaps i best get a standard phone and hac to te keyboard so that from a seperate circuit i can make alli want !