The Vodafone K3765 also has a connector for an external antenna, however it is covered by the housing and requires drilling to make it accessible (see pictures at the bottom of
Huawei K3765-HV (Vodafone) - 3G modem wiki).
Alternatively you could pick up one of those unlocked 3G-sticks Vodafone are currently selling in their shops for just € 10 including a Vodafone Websessions SIM and vouchers for 3*1h internet access (
http://www.prepaidgsm.net/forum/mobi...-new-post.html). Vodafone have the best 3G-coverage in Germany and their prepaid internet rates are more expensive, but still affordable for shortterm use (
Germany - Vodafone Web Sessions - Prepaid Wireless Internet Access). What I like about Vodafone's Websessions is, that you don't need to care about topping up credit as you can pay each session by credit card. Unfortunately they block VoIP.