How to dial a plus sign"+",

hi. seems a rare situation
I’m using asterisk+sangoma A101+orion T1 gsm channel bank to send calls to gsm network.everything works fine when i dial local or mobile numbers in ordinary format of 09XXX… . the issue is dialing international numbers which are only accepted by the operator in form of +97xxx… I’m aware that i can use 00 instead of + but the operator does not accept it. i’ve used lots of combinations. none worked. i’m pretty sure my extension configuration for calls to uk should be as following:

exten=>_[0-9].,1,Dial(dahdi/g1/+44${EXTEN:4}) exten=>_[0-9].,n,hangup()

when users dial 0044x… but it doesn’t work.
i don’t know if the problem is from asterisk (maybe it doesn’t see the plus sign as a dialed character and see it as a reserved function. the other possibility is that the sangoma card can not pass the + sign. i dont know what kind of signaling it uses to pass the dialed number. the link of sangoma and gsm channel bank uses D4 framing,B8ZS coding and E&M signaling and it works for local numbers.
any idea?