diff --git a/mgw_nat.app b/mgw_nat.app
new file mode 100644
index 0000000..4e61be2
--- /dev/null
+++ b/mgw_nat.app
@@ -0,0 +1,23 @@
+{application, mgw_nat,
+	[{description, "Media Gateway NAT"},
+	 {vsn, "1"},
+	 {modules, [mgw_nat_app, mgw_nat_sup, mgw_nat_usr, mgw_nat]},
+	 {mod, {mgw_nat_app, []}},
+	 {env, [
+		% SCCP rewrite
+		{real_hlr_gt, [6,3,9,1,8,0,0,0,4,0,1,2]},
+		{nat_hlr_gt, [3,5,4,8,9,0,0,0,7,1]},
+
+		% ISUP rewrite
+		{msrn_pfx_msc, [3,5,4,8,9,0,9,9]},
+		{msrn_pfx_stp, [6,3,9,2,9,9,4,2,0,0]},
+		{intern_pfx, [6,3]},
+
+		% SCTP / IP config
+		{msc_local_ip, any},
+		{msc_local_port, 2904},
+		{msc_remote_ip, {172,16,1,81}},
+		{stp_remote_ip, {172,16,249,20}},
+		{stp_remote_port, 2904}
+	  ]}
+]}.
diff --git a/src/mgw_nat.erl b/src/mgw_nat.erl
index 0518371..b35b763 100644
--- a/src/mgw_nat.erl
+++ b/src/mgw_nat.erl
@@ -102,14 +102,13 @@
 % Actual mangling of the decoded SCCP messages
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
--define(REAL_HLR_GT,	[6,3,9,1,8,0,0,0,4,0,1,2]).
--define(NAT_HLR_GT,	[3,5,4,8,9,0,0,0,7,1]).
-
 mangle_rx_called(from_stp, Addr = #sccp_addr{ssn = SSN,
 					     global_title = GT}) ->
+	{ok, RealHlrGt}  = application:get_env(real_hlr_gt),
+	{ok, NatHlrGt} = application:get_env(nat_hlr_gt),
 	case {SSN, GT#global_title.phone_number} of
-		{?SCCP_SSN_HLR, ?REAL_HLR_GT} ->
-			GTout = GT#global_title{phone_number = ?NAT_HLR_GT},
+		{?SCCP_SSN_HLR, RealHlrGt} ->
+			GTout = GT#global_title{phone_number = NatHlrGt},
 			io:format("SCCP STP->MSC rewrite ~p~n", [GTout]),
 			Addr#sccp_addr{global_title = GTout};
 		_ ->
@@ -120,9 +119,11 @@
 
 mangle_rx_calling(from_msc, Addr = #sccp_addr{ssn = SSN,
 					     global_title = GT}) ->
+	{ok, RealHlrGt} = application:get_env(real_hlr_gt),
+	{ok, NatHlrGt} = application:get_env(nat_hlr_gt),
 	case {SSN, GT#global_title.phone_number} of
-		{?SCCP_SSN_MSC, ?NAT_HLR_GT} ->
-			GTout = GT#global_title{phone_number = ?REAL_HLR_GT},
+		{?SCCP_SSN_MSC, NatHlrGt} ->
+			GTout = GT#global_title{phone_number = RealHlrGt},
 			io:format("SCCP MSC->STP rewrite ~p~n", [GTout]),
 			Addr#sccp_addr{global_title = GTout};
 		_ ->
@@ -148,10 +149,6 @@
 % Actual mangling of the decoded ISUP messages 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
--define(MSRN_PFX_MSC,	[3,5,4,8,9,0,9,9]).
--define(MSRN_PFX_STP,	[6,3,9,2,9,9,4,2,0,0]).
--define(INTERN_PFX,	[6,3]).
-
 % iterate over list of parameters and call mangle_rx_isup_par() for each one
 mangle_rx_isup_params(_From, _MsgType, _Msg, ParListOut, []) ->
 	ParListOut;
@@ -181,9 +178,12 @@
 	case NumType of
 		?ISUP_PAR_CALLED_P_NUM ->
 			% First convert to international number, if it is national
-			Num1 = isup_party_internationalize(PartyNum, ?INTERN_PFX),
+			Num1 = isup_party_internationalize(PartyNum,
+						application:get_env(intern_pfx)),
 			io:format("IAM MSRN rewrite (STP->MSC): "),
-			isup_party_replace_prefix(Num1, ?MSRN_PFX_STP, ?MSRN_PFX_MSC);
+			isup_party_replace_prefix(Num1,
+						application:get_env(msrn_pfx_stp),
+						application:get_env(msrn_pfx_msc));
 		_ ->
 			PartyNum
 	end;
@@ -193,9 +193,12 @@
 	case NumType of
 		?ISUP_PAR_CONNECTED_NUM ->
 			io:format("CON MSRN rewrite (MSC->STP): "),
-			Num1 = isup_party_replace_prefix(PartyNum, ?MSRN_PFX_MSC, ?MSRN_PFX_STP),
+			Num1 = isup_party_replace_prefix(PartyNum,
+						application:get_env(msrn_pfx_msc),
+						application:get_env(msrn_pfx_stp)),
 			% Second: convert to national number, if it is international
-			isup_party_nationalize(Num1, ?INTERN_PFX);
+			isup_party_nationalize(Num1,
+						application:get_env(intern_pfx));
 		_ ->
 			PartyNum
 	end;
@@ -203,7 +206,8 @@
 mangle_isup_number(from_msc, ?ISUP_MSGT_IAM, NumType, PartyNum) ->
 	case NumType of
 		?ISUP_PAR_CALLED_P_NUM ->
-			isup_party_nationalize(PartyNum, ?INTERN_PFX);
+			isup_party_nationalize(PartyNum,
+						applicaiton:get_env(intern_pfx));
 		_ ->
 			PartyNum
 	end;
@@ -212,7 +216,8 @@
 							   MsgT == ?ISUP_MSGT_ANM ->
 	case NumType of
 		?ISUP_PAR_CONNECTED_NUM ->
-			isup_party_internationalize(PartyNum, ?INTERN_PFX);
+			isup_party_internationalize(PartyNum,
+						application:get_env(intern_pfx));
 		_ ->
 			PartyNum
 	end;
diff --git a/src/mgw_nat_app.erl b/src/mgw_nat_app.erl
new file mode 100644
index 0000000..6b43a94
--- /dev/null
+++ b/src/mgw_nat_app.erl
@@ -0,0 +1,11 @@
+-module(mgw_nat_app).
+-behavior(application).
+-export([start/2, stop/1]).
+
+start(_Type, _Args) ->
+	Sup = mgw_nat_sup:start_link(),
+	io:format("Sup ~p~n", [Sup]),
+	Sup.
+
+stop(_State) ->
+	ok.
diff --git a/src/mgw_nat_sup.erl b/src/mgw_nat_sup.erl
index 3b7fd99..2dfe245 100644
--- a/src/mgw_nat_sup.erl
+++ b/src/mgw_nat_sup.erl
@@ -24,19 +24,17 @@
 -export([start_link/0]).
 -export([init/1]).
 
--define(MSC_LOCAL_IP,		any).
--define(MSC_LOCAL_PORT,		2904).
--define(MSC_REMOTE_IP,		{172,16,1,81}).
--define(STP_REMOTE_IP,		{172,16,249,20}).
--define(STP_REMOTE_PORT,	2904).
-
--define(SCTP_HDLR_ARGS,	[?MSC_LOCAL_IP, ?MSC_LOCAL_PORT, ?MSC_REMOTE_IP,
-			 ?STP_REMOTE_IP, ?STP_REMOTE_PORT]).
-
 start_link() ->
 	supervisor:start_link({local, ?MODULE}, ?MODULE, []).
 
 init(_Arg) ->
-	MgwChild = {mgw_nat_usr, {mgw_nat_usr, start_link, [?SCTP_HDLR_ARGS]},
+	{ok, MscLocalIp} = application:get_env(msc_local_ip),
+	{ok, MscLocalPort} = application:get_env(msc_local_port),
+	{ok, MscRemoteIp} = application:get_env(msc_remote_ip),
+	{ok, StpRemoteIp} = application:get_env(stp_remote_ip),
+	{ok, StpRemotePort} = application:get_env(stp_remote_port),
+	SctpHdlrArgs =	[MscLocalIp, MscLocalPort, MscRemoteIp,
+			 StpRemoteIp, StpRemotePort],
+	MgwChild = {mgw_nat_usr, {mgw_nat_usr, start_link, [SctpHdlrArgs]},
 		    permanent, 2000, worker, [mgw_nat_usr, sctp_handler, mgw_nat]},
 	{ok,{{one_for_all,1,1}, [MgwChild]}}.