Para editar a quantidade de mensagens que serão salvas no telefone (sendo o limite 999 itens), é muito fácil!

Faça o seguinte:

procure o arquivo private\10202BE9\101F87EB.txt, a estrutura dele é basicamente esta:

cenrep
version 1
[owner]
0x100058CD
[defaultmeta]
 16777216
[platsec]
 cap_rd=alwayspass cap_wr=WriteDeviceData
[Main]
0x1 int 20 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0x2 int 1 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0x3 int 2 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0x4 int 2 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0x7 int 0 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0x8 int -1 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0x9 int 0 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0xA int 64 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0xB int 1 16777216 cap_rd=alwayspass cap_wr=WriteDeviceData
0xC int 5 0 cap_rd=alwayspass cap_wr=alwaysfail
0xD int 8 0 cap_rd=alwayspass cap_wr=alwaysfail
0xE int 4098 0 cap_rd=alwayspass cap_wr=alwaysfail
0xF int 7 0 cap_rd=alwayspass cap_wr=alwaysfail
0x10 int 4101 0 cap_rd=alwayspass cap_wr=alwaysfail
0x11 int 4100 0 cap_rd=alwayspass cap_wr=alwaysfail
0x12 int 4099 0 cap_rd=alwayspass cap_wr=alwaysfail
0x13 int 6 0 cap_rd=alwayspass cap_wr=alwaysfail
0x14 int 4104 0 cap_rd=alwayspass cap_wr=alwaysfail
0x15 int -1 0 cap_rd=alwayspass cap_wr=alwaysfail
0x16 int -1 0 cap_rd=alwayspass cap_wr=alwaysfail
0x17 int -1 0 cap_rd=alwayspass cap_wr=alwaysfail
0x18 int -1 0 cap_rd=alwayspass cap_wr=alwaysfail
0x19 int -1 0 cap_rd=alwayspass cap_wr=alwaysfail
0x1A int -1 0 cap_rd=alwayspass cap_wr=alwaysfail
0x1B int -1 0 cap_rd=alwayspass cap_wr=alwaysfail

Na linha 0x1, podemos ver que o valor ali presente é 20. Significa, então, que será salvas no máximo 20 mensagens. Para aumentar, é só alterar valor para qualquer outro que não ultrapasse 999 (o limite).

Salve o arquivo e está tudo pronto.