"50 millisecond delay"

You will need to read the specifications for your particular phone system to determine the actual timing requirements for your particular application - do not just assume that 50ms is OK for any phone system anywhere in the world!

You will also need to determine the inter-digit timing requirements.

For the UK, the specs can be found at:
http://www.sinet.bt.com/351v4p1.pdf - see section 4.2

Of course, in this day and age, some systems may not even accept Pulse (or "Loop-Disconnect") dialling at all!

Here's some background & historical info: http://www.8052.com/forum/read.phtml?id=46429

BUT BEWARE: In some territories it is ILLEGAL to connect anything to the PSTN unless you have been through the appropriate Approvals process; it may not be sufficient that your product just meets all the standards - you may have to have the right piece of paper from the right test lab to prove it!

This has all been discussed many times before - you should use the 'Search' facility.

Here's a few examples:

8052.Com Message Forum: RE: 8880 DTMF transceiver and Call Progress

8052.Com Message Forum: Legal & Regulatory Issues

8052.Com Message Forum: RE: telephone interface:

and many, many more...!