Why some mobile numbers can't be dialed from PN Landline?

[#1]

Apparently certain Lyca numbers are treated as overseas ( Jersey based) mobiles and are not recognizd as local UK numbers. See here http://forums.moneysavingexpert.com/showthread.php?p=30882147

[#2]

@Dev,
Thanks for the link to discussion forum.  I have read it.  I don't think it applies to me.  We are dialing from Landline to mobile which does not have 074 number but the number was ported to Lyca from O2 (which is 077 number).  So, mobile to mobile is fine.

[#3]

Hi, I'm still picking this up from our side and will let you know whenever I have any further info, thanks.

[#4]

Hi Ben,
Thanks. 

[#5]

Hi all,
This is an update on the issue I had.  As of yesterday late afternoon, after receiving a call on my mobile from BT the issue has been resolved.    We believe the issue was with local network/swtiching linked to my landline.  But we still await what BT have to say.
Grand job done by PN Customer Support.  People concerned in resolving my issue have been congratulated and thanked. So, Well Done Support Guys.
Incidentally, I went over to Lyca Mobile because they offer much cheaper calls abroad as compared with major service providers in the UK and they only do PAYG so there is no worries about contract etc.  Every on-line top up also attracts additional credits in your account; so, this can't bad. 
Thank you all.
Regards,
Chandu.