Hello Mike, at first, i did not get your reply form mailinglist. found it only on web archive of mailinglist. other responses are comming to me well.
At second, u can define any tlv at kannel.conf and they will be passed withouth warning or error to smsbox and can be readed as metadata at DLR callback url. Definition for example: group = smpp-tlv name = tlv_source_network_type tag = 0x000e type =integer length = 1 smsc-id = smsc_id_where_it_comes Slavoj.
