A thank you note

Port of my landline number to VoIP completed a few days ago, ceasing my old FTTC line along the way. Took 10 days from request to implementation, and all went smoothly. I just wanted to say thanks to all of the several posters on a number of different threads who between them helped me to piece together the jigsaw of how this process works, or quite often doesn't, and avoid the various pitfalls. I now finally have the setup I've wanted for a while, but haven't till now been able to achieve.

I expected the dialtone to disappear on the PSTN phone connection, but it's still there, and 17070 says it has a different number. Could I use it and somebody else would get billed?

Also, just out of curiosity, how does incoming call routing to a ported number work these days? In the early days of number porting, I vaguely remember it was done by forwarding. Calls were initially routed to the network identified by the 5 digit prefix, which forwarded it on to the network to which the number had been ported. But I seem to recall Ofcom were at one stage keen to introduce direct routing, whereby each network keeps routing tables (at least of exceptions) and sends calls directly to the destination network. But the telcos didn't like it due to implementation cost.

There was a company called something like Atlantic Telecom I think, which went bust and stopped forwarding calls. So even its ex-customers who had ported their numbers away could no longer receive incoming calls. I think avoiding that and similar scenarios was part of Ofcom's motivation. This must all be getting on for 20 years ago now.

I expected the dialtone to disappear on the PSTN phone connection, but it's still there, and 17070 says it has a different number. Could I use it and somebody else would get billed?

The port has been renumbered, possibly an engineering number, until required elsewhere

Thaumaurge

If the number block it is in was owned by a BT PSTN switch it would be routed to that switch. This would add the porting prefix for the operators call handler (switch or software identity) and drop the call back to the previous (trunk) switch (all signalling no voice path). This would route the prefix to the correct operator. Calls from the ported operator are meant to be routed direct as they should know they have control of the number. (Tromboning calls is expensive to encourage this!)

Once enough of a number block has been moved to a BT VOIP switch the block would be routed to the VOIP switch. In theory the block could be only 10 numbers but more likely 1000 due to a limitation on the number of blocks a TDM switch can handle.

Other operators may have different ways of handling ported numbers depending on their call handlers.

OFCOM want to move to a database that each operator would interrogate to route direct, but I do not believe this is up and running yet and it would only apply to non PSTN switches. (Mobiles could be doing this already as the call handlers (Home location registers) are all based on VOIP call controls.)

If enough of the number in a block are ported to the same operator in theory the whole block can be migrated to the new operator and the remainder ported back BUT this is rare except with business number blocks,