ok after looking around can somone confirm that to connect a normal pstn phone to a asterisk box i would need a TDM card with a fxs port, one for each phone
also can i migrate me currect ddi from the isdn30 to a sip trunk provider?
the tdm route is correct, however, if you have a lot of estensions you will need a lot of cards.
You could also try ATA’s - more wires, but it will work.
As for numbers, you should be able to port number to a voip ITSP. I use voipfone and they charged £20 per line (assuming you are in the UK). I would look at IAX providers, instead of SIP, if possible