By default, when you send a text the sending number is set to our equipment number which is on ManxTelecom. This is the number which will appear on the recipient's phone and will be used if they reply. This number is a UK number, in that it begins with 44, but please note that some networks treat this as an international number.

447797805460 - Old relpy number on Jersey Telecom
447624800500 - New reply number on Manx Telecom

You can, of course, change your account so that the sending number is set to your own mobile number. In which case this will appear on the recipient phone. Of course if you are known to the recipient and they have put your number in their phonebook, the phone will change the number into your name.

In either the case the cost of the reply will be the standard charge made by the network for sending a text message.